I'm not familiar with that program at all, unfortunately, but I'd say work your ass off at grades and keep reapplying. In terms of when you can reapply, I'd do it at the next opportunity (preferably after showing significant improvement), but I'll defer to someone with more experience. Don't give up though. There's a guy here who applied three times to get accepted into the Marine Corps for OCS and he's doing quite well at API. The biggest thing is don't get discouraged. You're only a junior so you have time to improve.