Salaam sis.
I'd like to stress on the most important thing. Do not feel disheartened.
These exams come and go, just have faith and trust in God. InshaAllah khair.
I'd suggest repeating C3, 90% and above is required in C3 and C4 in order to get an A* and your aim must be high. Math requires non-stop practice and that's what you should be doing. My friend got an A in C3 and she didn't repeat so she ended up with a B.
So,
focus on improving on C3 and C4 mainly.
As for Chemistry, everything in each unit is a repeat of the same basic concept. Since you'll be giving Unit 5 and Unit 6. Might as well give Unit 4. You have a practice on how the paper will be. So, just do it.
Physics Unit 4 isn't hard but it's quite tricky. Thorough revision and practice is required for it.
For Chemistry and Physics, I'd say keep reading the text book until you have the concepts stamped into your head. It won't be easy but you can do it, I am sure of it.
So, henceforth ... I'd suggest you repeat them all. Aim high and work hard and stay focused , you can do it.
May Allah (SWT) make this easier for you and keep you strong, InshaAllah!
Good luck, sweetheart.