Having a nomination of any type is key so congratulations on achieving it. No one on the forum can tell you about your 'chances' -- just USNA Admissions. Technically, there are 20 slots defined for this particular category (which includes ROTC too), but that number will not likely give you any more insights into your chances. NAPS and sailors do not typically compete in this category. Army ROTC honor schools can compete in this one (if that was your meaning).
I also recommend that you have a good Plan B & C in place. With my students, I define Plan "B" is one or several ROTC scholarships, and then "C" is the set of civilian universities that you apply to as part of the ROTC application process. I have had four students who won a scholarship or simply joined ROTC on campus (as part of Plan C) and then won an appointment (4 of 4) the following year. Some 25 - 30% of all cadets/mids at the SAs did not come directly out of high school as many attended a prep school, or a year or two of college, prior to becoming cadets/mids.
Good luck with your Navy pursuits!