They always tell you to take the most advanced classes offered at your high school. It sounds like you are already doing that. Five or six core academic classes (math, science, history/social science, foreign language, English) is the norm for most USNA applicants. So if you are going down from 8 to 7 core classes, or from 7 to 6 core classes, that sounds fine. (I'm a little surprised your high school allows you to load up like that to start with, actually.) As 2018midmom said, you will want to always include at least one math and one science class on your schedule, but it sounds like you had three science classes so you can let one go.
The key is to push yourself, BUT also not bite off more than you can chew. Your idea to scale back slightly so you can give your best effort in academics and extracurriculars is a good one. Moreover, sometimes less really is more. If I looked at a transcript and saw that you were taking 3 science classes at once and 8 classes overall, I would actually wonder if (a) those courses had any rigor in them; and (b) if you would be able to retain information with that heavy a course load.
