Hi
First of all I’m sure university will be different. It is a fresh start and a place where all first years will be new. I would say though don’t take a course that you may not like because you are setting up your future and may not find people like you because you are not doing a course you like
Even at a grammar school, the teachers are there to help and who cares what anyone else thinks (I know this is easier said than done) but you just have to think you probably won’t see them again after you leave. If you need help definitely ask for it - it is your future and nobody will think you are stupid
Your past experiences probably lead to your anxiety around new people. Start with a hello and gradually build up
You’ll get there 😀