For the Air Force, it doesn't matter what your grades were in HS, for an ROTC pilot slot they look at your GPA I. College, and you compete for the slot at the beginning of your Jr year, so you only have your freshman and sophomore years to knock out a good GPA. There are also a battery of aptitude tests as well. But if I were in your shoes, I'd look at a guard or reserve unit and compete for one of their pilot slots, that way you know what airplane your getting when you start pilot training. I'm pretty sure there are navy and USMC guard or reserve units too, you have to do a lot of research and shop around.