I got one of those about three years ago, the way they did it in my unit (one of the largest in the nation) is they sent up all qualifying college program students to NETC for the national 3-year scholarship and whoever didn't get that was considered for the PNS scholarship. My stats weren't overwhelming, 2.9 first semester gpa, sat high pfa (under the old system, adjusted for today's standards it would probably be a good high). However, I got picked up over someone with a 3.6 simply because I had a better attitude than her and the staff knew that and took it into account when they awarded the scholarship.
Bottom line, if you have started taking the calc/physics required of scholarship mids, make in the neighborhood of a 3.0, have a commissionable pfa score, and don't have any aptitude problems you should be good to go.
PS-Make your own decision about this one, but I told them that I would have difficulty paying for school if I didn't get that PNS ride.