Schools vary in quality, top of the leagues to the bottom.
Some schools have exceptional results some have dire results.
However if you hate the environment it may well affect your learning.
You might be better going to a sixth form college and retaking GCSEs ?
This works well if the school environment just isn’t “you” and a more relaxed environment suits you.
Some exam boards are “harder” than others, but few universities or employers care what board gives the certificates. Unis don’t care about GCSE grades, (bar English and Maths) they care about A levels.