I wouldn't worry about Freshers week too much if it's not your sort of thing. For some people, it's great, and they can get drunk and aprty like never before. For others that aren't so keen on that sort of thing, it's not, but that doesn't matter.
You'll probably make most of your friends on your course, and a lot of the people you might meet at Freshers week you probably wont see much or again. If you dont like or dont feel comfortable at parties, no reason to go - there's plenty of other things to do, and there's plenty of other people that are similar. Plus, once your course starts, you'll soon make even more friends and fit in easily, it happens, no matter how shy or quiet you are.
If some events sound interesting or appealing, jump in and go there and enjoy it. If they don't and you'd rather not go, then don't force yourself to do something you probably wont enjoy. There'll be plenty of other oppurtunities to make friends, meet people and have a great time!
While some students get drunk, particularly in freshers week, a lot don't. People are different, and at university, there's all types. The ones going out and geting drunk may be more visible, but it doesn't mean that all students are like that, because they aren't.
It'll be fine, don't worry about it, and in no time, you'll meet lots of people like yourself and make some great friends
