I surprisingly LOST 15 pounds when I was at college. My program was only 1 year and I opted to live in the dorms because home was 2.5 hours away and the campus was a 5 minute walk.
I started eating better and working out in 2nd semester - I would run on an elliptical 1 hour a day and 'eat healthy'. It's hard to eat healthy on campus, especially with all the pizza, booze and snacks. Our campus had a new 'healthy eating' program which had a subway on campus, and the cafeteria's also provided healthy wraps, salad bars, smoothie stations, etc.
My program was pretty hard so I didn't have the chance to join clubs or anything, but I took that 1 hour a night off from doing homework or projects and it helped relieve a lot of stress.
My dorm room consisted of a single bed, a mini fridge, a desk and closet. Nothing more. So whenever I had a craving, I had to go down 5 floors (or across campus) to get food. I used to allow myself 1 treat a week (either a bag of chips, cookies, icecream, chocolate bar, etc) and that was my reward for eating healthy and being active.
When I started college, I was 200lbs, when I left 8 months later, I was 185. I was thrilled! But then I moved back home and returned to my mother's cooking...I put the weight back in within the next 6 months
Just keep motivated and don't let those skinny girls get to you. If you've made some good friends, they'll support you through your journey. (And we here at 3FC will too!!)