take it from someone who just got done with freshman year of college:
join gym immediately! always make time for working out, bc once you start skipping here and there, its easy to nearly stop altogether.
eat healthy! and dont eat when your bored... i try to stay away from snacks in my dorm--besides granola bars and the such.
drinking on the weekends ok (well maybe not legally), just dont get caught up with partying every night, thirsty thursday, etc etc. stay focused on your goals: education, staying in shape, not getting fined or facing jail time!
find friends who enjoy active activities that you like: basketball, lifting, tennis, running, anything that gets you moving
the freshmen fifteen plagues those who already werent very active. add in drinking, snacking, studying (inactivity), and it easily leads to fifteen or more pounds. you seem like your on top of things, so i wouldnt worry too much. i started lifting in college and ending up getting the freshmen fifteen--fifteen pounds of muscle!! (almost)