If you're a self-motivated person, meaning you're really considering quitting CA to concentrate on studies, go ahead.
If you're half-hearted, you think CA is important too, then balance it out.
Play twice a week. Saturday and Friday.
As for studying, I find that writing down everything you have learnt, be it from PPT slides or textbook, into an A4 piece of paper helps in re-inforcing your memory.
People usually say studying and music don't mix. You simply won't be able to concentrate. But I find music a good distraction. In your O levels, especially your first test, it won't be so slack and easy. It'll be tense. So studying with distractions sometimes is okay.
What is not okay is Mugging.
Mugging basically means going 5 hours without breaks, just reading and reading.
Well, it's bad for your brain.
What you should do is study with someone else. Pick a spot, [changi airport usually crowded nearing the Os], maybe go to some far away place with a good friend. Study under the block. Take bus home, come home, shag already, go sleep.
I once got this friend, Farhan. We both Farhans. Same school, class, tuition. We before exams go to tuition half hour early sit below block there study chemistry sia xD And then when in class, if you know something, and your friend doesn't, you try solve his problem. If you can, means you good already.
I remember last year I study in front of TV from 12-2am every morning. Then after school stay back for night class. 7-9.30pm.
Make sure to give yourself a break though. You are not a machine, no one is
If you feel stressed, go catch a movie. I advise against CA, since CA doesn't really release stress that much. Go outside interact with friends la, eat dinner all this.
If you study consistently, there is nothing to be afraid of.
Make sure when you enter exam hall, you know 100% of everything you need to know for that test.
O Level got a lot of tricky question to distinguish which students are diligent and which are smart.
Most average students can get answer to a particular Qn correct, but they also look out for your phrasing, etc.
After all, english originated in british =D which is where Cambridge is .
TL;DR
Study consistently, don't push too hard on yourself, ask for 1 on 1 session with teachers.
It's good that you're already starting to think of studying for O levels, but srsly, don't overdo it.
P.S 1 perm gun is $37 , I dnt think anyone besides your parents/girl will spend that much on you lah
All the best to you and your future endeavours buddy.