Dear everyone, I am here to seek for your kind help in checking the sentences below which are about if-clauses.

1. If only I had paid more attention and effort in the past, I could have already entered any of those famous universities like my old friends.

(I wrote this with the notion of expressing my regrets of not working hard in the past and therefore cannot enter a good college now) (Incidentally, does college means the same with university?)

2. Given the situation that my friend is talking about his past, when he took two significant exams on the same day, and I reply:

2.1. If I were you, I would have been very nervous about that and might even be crumbled.
2.2. If I had been you, I would have been very nervous about that and might even be crumbled.
2.3. If I were you, I would be very nervous about that and might even be crumbled.

(I wrote this with the idea of expressing that if I were him at that period of time in the past, I might have collapsed at that time since the pressure might be too much for me to manage and the schedule could be fairly tight.)

Actually, I learnt the if-clause grammar on this page:

However, it just showed us 3 types of straightforward structures and usages, but never said that we could mix them up for different purposes, such as talking about the past while pretending yourself with another person just like the instances I made in question 2. So, are we able to mix them up? To combine a part of the structure in usage 2 and usage 3, mentioned in the link I provided, in a sentence together?

Thank you very much indeed for the help. I endeavour to learn better English and you have just helped me on my way.
2.1 "works", but it isn't very natural and not actually correct.

2.2 is correct.

2.3 is correct.
Thanks for the prompt reply indeed!

Concerning your comment towards 2.1, did you mean that it is not actually correct to mix the 3 different structures and usages of if-clause up?

Regarding 2.2 and 2.3, are they both grammatically correct and correct in meaning according to the notion that I was trying to convey?