While I do not mean to understate your intelligence, I must say that I'm fairly confident that no middle-school level advance-placement course will suffice as any sort of a stand in for any highschool level mathematics. Highschool is just a whole new ball game...
Honestly, Geometry was probably the most useless class I ever took. It's not that it's stupid or completely irrelevant, it's just that it's practical application to the real world pales in comparison to virtually every other form of math... Take it if you wish, but if you happen to really enjoy math, I might recommend that you take a different math course instead. You might find other math subjects a great deal more fulfilling...
If it is simply a "general science" course, it most likely is quite easy (and useless). However, you will most likely be fairly surprised initially at just how much more intense & difficult biology, or chemistry, or physics is compared to any other science courses you have taken in the past...And at that, highschool science courses are kindergarten reading compared to their university-level couterparts....
How about
: Don't.

Seriously, you are brand new to highschool. It is significantly different than middle school. Honestly, I think it is a bit premature to be already deciding that you can "easily master" your initial freshmen subjects. There is a fairly big jump in many ways from 8th grade to 9th grade, and you really do not know just yet what you are about to get into...
My suggestion is that you simply go along with the flow. Take the subjects that you would normally have to take as a highschool freshmen. If you are really as good as you thought you were, then this should very obviously be reflected in your grades, and your teachers will readily take the necessary actions to bump you up to the more appropriate learning level.. You won't need to do any of the work here yourself..
