I intended to perform the obligatory Hajj, myself and some of my work colleagues. Please note that I am a resident of Makkah al-Mukarramah. In fact we went out to ‘Arafah, then to Muzdalifah, but there I lost my colleagues, and I did not know the obligatory actions and rituals of Hajj, or what is prohibited during Hajj. When I lost my colleagues with whom I was walking, and who were going to teach me how to do Hajj, I went back to my residence in Makkah and took off my ihram. That was before half of the night had passed, and I did not complete the rest of Hajj.

What is the ruling on that? And what do I have to do?

Praise
be to Allah.

What is required of everyone who enters
ihram for ‘Umrah or Hajj is to complete the rituals, regardless of whether
he started an obligatory or supererogatory (naafil) pilgrimage, because
Allah, may He be exalted, says (interpretation of the meaning): “And
perform properly (i.e. all the ceremonies according to the ways of Prophet
Muhammad blessings and peace of Allah be upon him), the Hajj and Umrah (i.e.
the pilgrimage to Makkah) for Allah” [al-Baqarah 2:196]

Shaykh Ibn ‘Uthaymeen (may Allah have
mercy on him) said: 

If a person begins Hajj or ‘Umrah, it is
not permissible for him to stop it unless he has an excuse that prevents him
from completing the rituals, because Allah, may He be exalted, says
(interpretation of the meaning): “And perform properly (i.e. all the
ceremonies according to the ways of Prophet Muhammad blessings and peace of
Allah be upon him), the Hajj and Umrah (i.e. the pilgrimage to Makkah) for
Allah . But if you are prevented (from completing them), sacrifice a Hady
(animal, i.e. a sheep, a cow, or a camel, etc.) such as you can afford” [al-Baqarah
2:196]
. “But if you are prevented” means: if you are prevented
from completing the rituals.

End quote from Majmoo‘ Fataawa Ibn
‘Uthaymeen
(23/438) 

Losing your colleagues during Hajj does
not come under the heading of being prevented, because you could have
completed the rituals without them. What you should have done, once you had
decided to do Hajj, was to learn its rulings, especially since you are one
of the residents of Makkah and it would not have been difficult for you to
learn the rituals before starting it, or to ask about how to complete them
after having started. 

What you have to do now is the following: 

Firstly:

Repent to Allah for having fallen short in
performing the rituals in the proper manner because of not having learnt
about the religion even though the means of learning were readily available
to you. 

Secondly:

As you were either doing ifraad (Hajj on
its own) or qiraann (Hajj along with ‘Umrah), as appears to be the case from
your question, and because the people of Makkah cannot do tamattu‘ (‘umrah
followed by Hajj, exiting ihram in between), then there still remains for
you to do the pillars or essential parts of Hajj, namely tawaaf al-ifaadah
and the sa‘i of Hajj. These essential parts are not waived under any
circumstances. Based on that, it is essential for you to do them no matter
how long a time has elapsed. 

Shaykh Ibn ‘Uthaymeen (may Allah have
mercy on him) said: 

Tawaaf al-ifaadah is one of the pillars or
essential parts of Hajj, without which Hajj is not complete. If a person
omits it, then his Hajj is not complete and it is essential for him to do
it. So he should go back, even if he is in his own country, and do tawaaf
al-ifaadah. In this case, so long as he has not yet done that tawaaf, it is
not permissible for him to be intimate with his wife, because he has not yet
exited completely from his ihram (i.e., the second stage of exiting ihram).
That is because he has not exited completely from his ihram until he has
done tawaaf al-ifaadah and sa‘i, if he is doing tamattu‘, or if he is doing
qiraan or ifraad, but he did not do sa‘i with tawaaf al-qudoom.

End quote from Fataawa Arkaan al-Islam
(p. 541) 

Shaykh Ibn Baaz (may Allah have mercy on
him) was asked: I am one of the residents of Makkah. I did Hajj last year
and I did tawaaf, but I did not do sa‘i. What is the ruling? 

He replied: 

You have to do sa‘i, and this was an error
on your part. It is essential to do sa‘i, regardless of whether you are a
resident of Makkah or otherwise. It is essential to do sa‘i following tawaaf
after coming down from ‘Arafah; you have to do tawaaf and sa‘i. The one who
omitted sa‘i must do sa‘i now.

End quote from Fataawa ash-Shaykh Ibn
Baaz
(17/341) 

Thirdly: 

You have to offer compensation for the
obligatory acts that you omitted until the time for them was over by
offering a sacrifice. These acts are: stoning the Jamaraat, staying
overnight in Mina during the nights of at-Tashreeq, and offering a sacrifice
if your Hajj was qiraan. 

As to whether shaving the head or cutting
the hair are also included in that, so that you have to do offer a
sacrifice, or that is not the case, so you do not have to do that, this is a
matter concerning which the scholars (may Allah have mercy on them)
differed: 

The Hanafis, Maalikis and Hanbalis –
according to one report – are of the view that if a person delays shaving
his head until the days of sacrifice are over, he has to offer a sacrifice
to make up for that delay.

The Shaafa‘is, and the Hanbalis according
to another report, are of the view that if he delays shaving his head until
the days of tashreeq are over, he does not have to do anything, but any time
he does it, it is acceptable, like tawaaf al-ifaadah and sa‘i. The Shaafa‘is
stated that it is makrooh to delay it.

See: al-Mawsoo‘ah al-Fiqhiyyah
(10/12-13) 

The first view, which is that it is
obligatory to offer a sacrifice, was mentioned in fatwas by Shaykh Ibn
‘Uthaymeen. He (may Allah have mercy on him) was asked: A man did ‘Umrah or
Hajj, but when shaving his head, he did not shave all of his hair. Several
years have passed since his Hajj or ‘Umrah. What is the ruling on that? We
would also like to have a guideline on when the pilgrim doing Hajj or ‘Umrah
should be instructed, if he has omitted any of the rituals, to go back to
Makkah and do them. 

He replied: This man has omitted an
obligatory act, and omission of obligatory acts requires a fidyah (ransom),
which is a sacrifice that should be slaughtered in Makkah and the meat
distributed to the poor. Thus his Hajj will become complete. 

With regard to things that the pilgrim
must make up if he failed to do them, these are the pillars or essential
parts of Hajj. As for obligatory acts, if the time for them has ended, he
should make up for that by offering a sacrifice.

End quote from Majmoo‘ Fataawa Ibn
‘Uthaymeen
(22/481) 

Fourthly: 

With regard to the prohibited acts that
you have committed, such as having intercourse before completing your
rituals, you do not have to do anything, because what appears to be the case
is that you only did that because you were unaware of the ruling. 

For more information, please see the
answer to question no. 40512 and
176329

To sum up: 

As well as repenting, you have to hasten
to complete your rituals by doing the essential parts that still remain,
namely tawaaf al-ifaadah and sa‘i of Hajj. You also have to offer three
sacrifices to be slaughtered in the sanctuary and the meat distributed to
the poor there, to make up for the obligatory acts that you omitted, namely
shaving the head, stoning the Jamaraat and staying overnight in Mina. You
should also offer a fourth sacrifice, namely the hadiy if you were doing
qiraan. If you cannot afford to do that then you must fast for ten days. 

And Allah knows best.