I'm also a fresher at Lancaster - I was never a big drinker and had never been on a night out before drinking until this week. Psychologically, in social situations, people tend perceive those who say yes to things as more approachable, however if they make you feel really uncomfortable then don't feel pressured to do so. This week, I've said yes to a lot of things that I wouldn't otherwise usually want to do but I'm glad I did. I was really scared that I wouldn't get along with my flat but I think we all get on quite well. I agree that the freshers reps seem to only be interested in drinking and partying and if you don't they just sort of shun you a bit. Our freshers rep is only interested in the drinking events and hasn't really told us about anything else that went on during the week, we pretty much did everything ourselves.
I think you once lectures get going you'll enjoy yourself more as you get to know your coursemates. If your flat just aren't your kind of people, it's fine! Just to be sure to make an effort with your coursemates or people from societies (if you want to join one) and approach them if everyone's waiting to go into a lecture theatre or whatever. If there are people sitting alone, go sit with them; ask them their name/college/if they know this or if they know that or where that is or if they're going to this. Once you touch on some common ground (like a TV show or music), just keep rolling with it. Keep smiling and be positive! You'll find something to bond over! Keep trying to talk to your coursemates and try finding one at your college so you have someone to go with. Have you tried going to some of the quieter nights or pub quizes? I went to the one at the Chaplaincy and they put people with others to fill up groups, so that might be a good place to meet friends if you love a good quiz..?