I would never say, "Don't come to NMMI." As the only college out there that receives sponsored Preps from the USMMA, we do have a strong relationship with them. However, we do not have a Navy ROTC program. Your Navy ROTC scholarship contract should allow you to break it to attend the USNA. In my initial post I did not say that if these contracted cadets had appointments to the USMA (not USMMA), there wouldn't have been any problems. "Army to Army" was OK. Army to anything else was a problem.
Without knowing your SAT/ACT scores or seeing your high school transcript, it would be difficult to advise you on what to do.