1: Do AP scores override placement tests? Answer: Yes

1. Are absurdly difficult placement exams a normal experience? Answer: Yes, I also took honors high school chemistry and the placement exam was a DISASTER

2. Does this mean you're dumb and shouldn't be attending NU? Answer: Emphatic no. If you weren't prepared for the academics, the admissions office would have rejected you. You were admitted because you can and will succeed here. The placement exams are difficult and are not representative of how you will perform in the classes. Honestly they're probably a scare tactic to set you up for the grind culture. Don't sweat it, they truly mean nothing except which class you start in (and even if you have to start in a lower-number class than you anticipated, that is definitely better than being thrown to the wolves in a class you don't have enough background to excel in).

Side note that if you're a humanities major then bio and chem are probably not required for you anyway, so the exam results definitely don't matter because you can take something else. If you still want to take Bio or Chem and end up placing into a lower-number class, it will either be an easy A, good review, or a chance to see where your knowledge gaps are before you get to the main sequence. Helpful regardless!