I know how you feel - I've spent a lot of time trying to be someone I'm not - I don't act myself for fear of being told off! But I am getting better.
Is it going to be your first year at uni? If so, will you know anyone? If not - I would say use it to your advantage - that is what I am planning to do! You get a completely clean slate! Or at least I'm hoping to do that!
But with the call centre, just try to persevere - you only have another month or so left! Talk to the girl next to you - she'll probably try to make sure you're involved in other conversations as well. Some of the reason you feel 'left out' is because you do what I do - go all quiet or pretend you're doing something else when people you don't know too well start talking to you. Perhaps try asking more questions other than the usual ones, and believe in yourself!
OK. Far easier said than done - I should know! But it's a step in the right direction.
Also, do try to talk to someone, since I think this would help you a lot - even if it's just because there's someone there to listen to you!
Hope this helps, and sorry to compare it to me - but it's the only way I could figure writing it in a coherent(ish) way!