I wish you the best of luck! I went through a similar thing where at AS I got BBCE (Biology Geology, Chemistry, Physics), my sixth form did not teach A2 Geology so I had to take Physics. At the end of A2 I'd got CCE and a B at EPQ. I'd already discussed retaking as my exams hadn't been going great and so I ended up doing a retake and an extra year at sixth form. I ended up with ABC, my A was extremely close to an A* and my C near a B. I did retake some of my AS exams so I actually have AAC in Biology, Chemistry and Physics AS. So don't worry about it, and if it comes to it having to retake your A2's can be upsetting but you will get through it.
For Physics I revised a lot through reciting my notes daily, doing past papers every day and I did end up getting a private tutor. I also went to revision sessions and really focused on my coursework - I got an A on my coursework! You've done amazingly at Maths so you should be fine.