What do you want to achieve at the end? Do you want more friends or do you want time alone to do your own thing?
If you want more friends then the opportunities are set out for you and your few friends seem like they actively want you to hang out with them. Take that opportunity and try to have fun. Even if you don't enjoy it that much just make a good impression so you have a few mates to talk to if you need to.
If you want to be alone, well just tell them you prefer being alone but for them to not take that personally. And do your own thing, although I wouldn't advise that as being lonely sucks after a while.
Good luck!