Hi there!!
It's so easy to put weight on when you're in college, I can certainly relate. It's also hard to resist the peer pressure when everyone around you wants to eat takeout food and go out all the time! Argh, I know that way too well...
Your best bet would be to watch your calories - cook at home if you can, and if you go out, try to either go to restaurants that have calorie values of food listed on the menu (Olive Garden, for example. I think McDonald's does that too?), or get a smartphone app for logging your meals - LoseIt! is a decent one for the iPhone. There are many more too, but most suck
You can also start a journal online - I did it, and it was a tremendous help for my weight loss!! There are decent free ones you can use, like MyFitDay or LiveStrong. They all have a food database that includes most restaurant foods, so if you want to know how many calories you are about to eat, you can search for that meal and find out.
Also, get into sports. University is perfect for that. I ran track back in my college days - it helped me lose 12 pounds, and also made me a little more popular
Good luck with everything!