The fact that you've managed to improve is great so have confidence in your ability.
I'm sure you'll improve even further at a-level! Think of how far you've come and how much you've achieved in a relatively short amount of time!
Being aware of what you're less confident at is a good sign as you'll know to pay more attention to it in the exam if it comes up. Don't think 'oh I might get this wrong' - a negative mindset does no one favours as you know that you CAN do these questions!
For circle theorems, go over the rules and make sure that you can recognise the different 'versions' (for lack of a better word) that the triangles can take in the circle. Haha, this probably sounds stupid, nvm.
You'll find out how well you did on results day - though true, looking at answers beforehand helps to reassure you. Just don't take other people's answers for granted : who knows, they might be in the wrong despite how confident they are - misreads of questions etc.
Just do your best. Screw grade boundaries.
It's something you can't prepare or revise for after all!
Good luck! Is it tomorrow?