Somethings you learn at A-level Physics are useful for the ATPLs. I've found it useful in M&B and POF. GCSE Math is good as algebra has helped me with calculations in the ATPLs such as manipulating forumlas. But it's all taught again in the ATPL manuals so it doesn't really matter.
Don't get down if your results aren't great either, education isn't for everyone, I have IGCSEs B-C, I left my 6th form about 2 years ago too as I didn't like a-levels. That's not to say I'm dumb, I happen to being getting through the flying studies quite nicely. The reason I was crap in school was because I spent so much time thinking about flying and reading aviation books rather than home work or daydreaming about me being interviewed by an airline in lessons. I'd actually read 5 of the PPL subjects at age 14-15. I started my PPL at nearly age 19 and focusing on aviation was more beneficial to my training than that Math homework I didn't do.
Don't work too hard, good qualifications are good to have but don't kiss your teenage life away either. No point having A* everything but having no social skills whatsoever.