I didn't study for even 1 of my GCSEs and I walked out with 8 As and A*s and 2 Bs
After that you realise, GCSE is like a pin drop compared to the beast that is A levels!! I study a lot now and barely scratch the surface. The thing is, GCSE isn't as important as teachers may mislead you to believe. As long as you pass 5 and pass English and maths, thats it. Unless you want to do science in college, its OK if you fail them all. I know someone who failed some sciences and got into a really good university in London for computing and business without ever having to face science again.
what I would say is, try to get a 5 or 6 for English and Maths because if Universities look at GCSEs, they most commonly want more than a pass for Maths and English., it'll help you set yourself apart from the rest. (for example the person I mentioned earlier had to retake Maths to get a B because a C wasn't enough for a good university)
PS- Prom for me was meh. I mainly went there for the unlimited cake and photo booth.