Best of the Village
Senior Linguistics Developer at Luminoso
Believe me, I have immense amounts of sympathy for you! When I was in high school, I took AP French, and I struggled with it. A lot. Every essay I wrote was an exercise in looking up every noun I used to find out whether it was masculine or feminine....
Of course, at this point, I have a degree in linguistics (and my job title is "Senior Linguistics Developer"), so clearly I can't be completely scared of languages. All the same, I'm still much better at the concept of language than I am at actually writing anything in French.
I'll second Monty's suggestion that talking to a school guidance counselor is a good idea: someone who knows you and knows what you're able to handle. I certainly will say that you shouldn't duck out of Spanish just because it's hard; tackling hard challenges is the best way to grow and feel fulfilled. But by the same token, I wouldn't recommend that you take a course in advanced nuclear physics this year just because it's hard!
I am certain, though, that if you take Spanish and you do well in it, you'll be glad that you did it. If nothing else, you'll always get to say, "Hey, I made it through AP Spanish! Hated it, forgot all of it, but by heavens I entered the dragon's lair and came out the other side, and that's an achievement." (Note: probably you shouldn't literally say that. People look at you funny when you talk about dragon's lairs.) But you'll probably get a lot more out of it than that.