sounds fun and I think that would be a great way to meet new people and boost your confidence! Kickboxing classes always have at least one mega hottie as an instructor, so there is a built-in motivator right there. LoL.
It always makes a girl feel better about herself to know she could beat up the guy talking to her, so that idea sounds A+ to me.
If anything else, you could try joining some of the clubs at your school or... *dun dun dun!* start chatting with people in your classes and go to the millions of campus functions and participate.
Hiding out in your room keeps your from being out and seen, so people won't get to know you because you aren't giving them a chance. It may be uncomfortable, but step out into the open and see what happens. I think you'll be surprised with how quickly people will accept you.