Joined the army reserve and haven't gone to army basic yet. Can I opt out?

Here's the deal: I joined the army reserve in may, went to MEPS and signed the contract. I am prior service navy (served 4 years got out in feb 2010 and was in inactive navy reserve till i joined the army reserve) and currently going to college on the post 9/11 G.I. Bill. The army told me that I had to go to army boot camp. I don't mind having to go to boot camp again, however at MEPs they assigned me Aug 01, which cuts out the last 2 weeks of my summer semester at college. I asked the person who wrote my orders if I could change it, and he said that when I get to my unit they could. I went to drill once and asked the sergeant in charge if he could change it. He refused to; his reasoning was that he didnt want to take the risk of me not going. I kept trying to explain to him that it interefered with my school. He didn't budge. What will happen if stop going to drill and don't go to boot camp?