Here's the deal . . .
First understand that NASS is a recruiting tool. Priority usually goes to applicants who are from schools or areas of the country that historically have not sent a lot of students to USNA. The idea is to get the word out about USNA to people who may not be familiar with it.
Second, because of the above, the most qualified candidates don't always get accepted. You may be the best candidate in the country, but if you attend a school that usually sends several students to USNA each year, you may not get into NASS. Like STEM camp, it's not a pure meritocracy. Thus, failing to be accepted to NASS is not necessarily predictive of your chances as an applicant to USNA.
Third, the more NASS sessions you can potentially attend, the more likely you are to be accepted. I don't want to suggest the numbers will go up dramatically, but it definitely increases your odds, especially if you can attend Session 1, which typically is less "popular" because so many h.s. students are still in school. For those other than the OP, if you can possibly attend Session 1, apply for it as that probably gives you the best odds.
Fourth, if you are accepted to NASS, it is for a particular session. IOW, it's not like you are accepted and then get to choose what session you want. You MAY be able to switch sessions, but the ability to do so will depend on someone in the other session either dropping out or asking to switch to your session. While a few NASS folks are able to switch sessions after acceptance, I would NOT count on it.
Fifth, because of the above, if there is zero chance you can (or will) attend NASS for a particular session, then don't apply for that session. I do NOT recommend applying to a session you know you can't attend, hoping you'll be accepted to that session and then be able to switch. USNA doesn't have the time, energy or manpower to be trying to switch schedules for hundreds of candidates and you will likely find that you can't switch and now you have nothing. If you could juggle some stuff and maybe make it to a session, then apply.