Totally natural to feel like that. Don't try and think about all your worries at once. Enjoy the rest of your holidays - and concentrate on packing/preparing for moving. Don't think about the social stuff yet. When you're there, take it one step at a time. You can't solve all these worries at once - it will take a while to feel settled in all the aspects of your life that you've mentioned.
Also, make sure you give yourself breaks when you're there. E.g. if you're worried about the social side, and you've recently done some going out/being sociable with your flatmates, don't be worried about giving yourself a night off just to be by yourself.