I went into the NROTC program as a college pragram student (walk in midn), picked up my scholarship no problem (good grades and good prt scores - and I wanted it!) and had it for my soph-senior year. I just commissioned this past weekend and am headed to Pensacola in 2 weeks for flight school as a NA. You can definitely do it without having received the scholarship before starting the program.
Good Luck!
And feel free to PM me if you have any questions.
Btw, if you aren't 100% for the Academy, chances are its not for you. Plus college cant be beaten!