well i don't know if it's relevant, but in ITA last year I was averaging high 80s/ low 90s for my SACs, and even got like 68% in one of them. The exam came and I missed a question worth 3 marks, and screwed up a few others.
I ended up with a score of 47 lol
So to get a 50, you don't have to get perfect scores for everything. You can afford to lose 1 or 2 marks here and there, max.