First congrats on both graduation and selection in PG college. I am a UG in a residential college and I'll try to answer your somewhat broad question.
I generally don't fall apart while making a first friend in my school or college life.
Hopefully, you'd have an orientation week where you'll get plenty of chances to break the ice and activities which don't let you have awkward silences. Don't try to rub those interactions as "meh", "I don't want to do this. This is normie, we can have better discussions instead." Those initial days are for knowing people, not judging them.
However, I always was out of a group and felt it extremely difficult to get into any type of social groups within my batchmates.
Most PG students here normally hangout with their project guide's other students. So you'd have a group whether you want it or not. A lot of people also go work/study in public places where they get to meet other UG students who come there regularly. It can be a gym, cafe, library, etc.
If there are any posts open where student representatives are required, I suggest that you apply for those. If the only reason for holding yourself back is that you get nervous around people, go for it. You will benefit. I cannot emphasize it much.
For inside hostel activities, participate in celebrations, random time pass group discussions. Wave to people that you see often. There are plenty of questions here about small talk, socializing, etc.
You are not extraordinarily good in your academics maybe people will not be that interested in you.
This is true only when you're in a highly competitive environment like placements or resume making processes etc. Normally study groups/pairs are the best way to go of the end goal is the same. I am not great academically, but I do have friends in various batches because of other things, like interests, courses, sports, etc. Academia isn't your complete personality. It is the resulting lack of confidence that makes it worse.
May be if I am nauseating and vomit then people will always try to stay away.
Close friends are always there in hospitals or for running errands for you. Yes, not everyone could do that. All I can say is to offer help too.