Whoever circumambulates the Ka‘bah seven times, from the Black Stone to the Black Stone, his tawaaf is valid, but if he fell short of that, even by one footstep, then his tawaaf is not valid.
An-Nawawi (may Allah have mercy on him) said: If any of the seven circuits remains incomplete, then his tawaaf is not valid, regardless of whether what was omitted was small or great, and whether he is now in Makkah or in his homeland, but he is not obliged to offer a compensatory sacrifice. This is our view and it is the view of the majority of scholars.
End quote from Sharh al-Muhadhdhab (8/29)
Al-Hajjaawi said in az-Zaad: Whoever omits anything of tawaaf, it is not valid.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
“Anything” includes even if he omitted one step or one handspan of tawaaf; in that case it is not valid.
End quote from ash-Sharh al-Mumti‘ (7/249)
In order for tawaaf to be valid, it is not essential that the individual stand on the line, whether at the beginning or end of tawaaf. Rather if he comes in line with the Black Stone, then goes around seven times from the Black Stone to the Black Stone, then his tawaaf is valid.
Al-Hajjaawi said in Zaad al-Mustaqni‘: Then he should come in line with the Black Stone with all of his body.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: I have my reservations about the idea of coming in line with it with all of the body, because it seems that what the Sahaabah (may Allah be pleased with them) did is that when they came in line with it, that was either with the entire body or with the right side of the body or the left side, and the matter is not so strict. But according to the fuqaha’ this is essential. But then there is a problem: how is one to do that precisely? According to the author, the entire body must come in line with the Black Stone. However the correct view is that that is not obligatory and that if he comes in line with it, even if that is only with part of his body, then that is sufficient. This was the view of Shaykh al-Islam, and there is no need to come in line with it with all of the body, although if that is possible then it is undoubtedly preferable.
End quote from ash-Sharh al-Mumti‘.
Based on that, if the matter is as you describe, that you tried hard to figure out where the Black Stone is, and you did the best you could, then it does not appear to be the case that you have to do anything further, so long as you completed seven circuits from the Black Stone to the Black Stone, even if it so happened that you made a slight error at the beginning or end of one of these circuits, so long as you started tawaaf and ended it in line with the Black Stone, to the best of your knowledge.
With regard to your saying that your mahram cut your hair, there is nothing wrong with that. What is required is cutting the hair after finishing tawaaf and sa‘i. Whoever did that, it is a valid, whether he was in ihram for Hajj or ‘Umrah or not, if he was one of your mahrams.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If a woman cuts her hair herself, or a man shaves his head himself, or someone who is in ihram shaves it, or someone who is not in ihram shaves it, all of that is acceptable.
End quote from Majmoo‘ al-Fataawa (22/483).
And Allah knows best.