How can I burn more calories?

I am a college student (sopre, age 18) and although I walk to cl each day and walk around between cles, it's not enough exercise to burn off the calories I eat. I've restricted myself to eating only when I'm hungry, and choosing healthier items (veggie cup not chocolate, etc), but it's still not enough; clearly I need to up my exercise as well. However, I live off-campus, in a crappy community -- I literally cannot get up and take a walk in the middle of doing homework because I and my boyfriend are afraid of getting mugged by the various "characters" nearby. The apartment is minuscule, and I am poor; I cannot afford a treadmill to make a "walking desk" or any such thing. I don't drink or do any drugs; I just come home and sit and do homework with my BF. I'm at a loss for how to fix my overweight body, help :(