im no longer sure if i should continue with physics 3/4

As i decided to do yr 12 physics a year early, I am now beginning to regret it especially after seeing my end of yr exam score for unit 1&2 (39%). I struggled with unit 2 a lot, and most of my sac marks were around 50%, i feel as though i am the worst in my class, so at this point I'm contemplating whether or not I should just switch to another subject.