If you go for 11th grade, chances are they’ll ask for the ACT or SAT (PSAT maybe) rather than the SSAT. Even if not, I think a good score on one of these tests would really help you, so start prepping for those if you can. I had great ACT scores on file when I applied, and I definitely think those helped me stand out.
As someone said earlier, if you are committed to going to boarding school, you’ll need to diversify your list. When I was applying to boarding schools only a few years ago, places like Loomis and Taft were considered a half-tier below the places the Deerfield and Choate–definitely no longer the case. Look at places like Blair, Peddie, Kent, NHM, etc. All of those places can probably provide more programs than your current school, and are all fantastic opportunities.