"Average" typically results in a selection chance of around 37.48%. In all seriousness, I have no idea, I'm not familiar with NROTC in any way, but I assume if you want your question answered you could do a bit of research about what makes someone competitive. If you've already done this to no avail, you're probably going to want to include a lot more info about yourself other than "my fitness scores are average." There is a lot more that they're going to consider in addition to your fitness level, most notably grades, ACT/SAT, etc.