I think I might have failed the APUSH exam!?

Harriet Tubman was from further back yeah. Douglass I'm not sure. It's hard to know if it will cost you a passing grade or not because you don't say how you think you did on the other parts. Honestly I doubt that'll make or break you. If you're this concerned about how you did I'm guessing you were concerned enough to study and probably did alright on the other parts. Way back in the day (2007) I did an FRQ on some presidents or something and I didn't know a single thing, I BS'd it and I still got a 4 on the exam. You might be pleasantly surprised.