It's okay, I'm sure you did alright!
As for what you want, I would recommend getting a statement of marks which shows you where you lost marks on the exam (only useful for science + mathsy ones btw).
What you look for are these things:
1. Where did you lo
ose marks? Get a copy of the exam and look at where you lost them, try think of your answers
2. CHECK THAT THE MARKS IN THE COLUMNS MATCH! One time my teacher told me a story about how her son's paper was incorrectly marked. One examiner had given him full marks, while the other had given him a column of zeros, she suspected that the marker had missed a page - very rare, but does happen apparently.
Look of any discrepancies, then if you're really sure there is a mistake order a copy of your exam script (you can't actually buy it back, they even burn the copy then send you... ikr so serious). I say this is your last move because it can be a hassle as you have to get your principal to order it, supervising teacher, costs more money etc etc.
Good luck with it! Let us know how it goes
EDIT: typos, as it seemed to annoy a certain someone