gcse exams as someone who isnt naturally smart (how to revise?)

i’m dyslexic and am not naturally smart i work so incredibly hard but my grades don’t represent that AT ALL. for my first gcse i worked for 3.5 hours (or more) EVERDAY for about 5 months i got a grade 4. my friend started revising a month before and got a 7?. but like i swear i knew everything like how did i get a 4????? is there any alternative ways to revise (i used flash cards, videos, mindmaps, reading notes, hi lighting textbook active recall stuff) but my grades are so low for the amount of work i put in it makes me so upset and i feel i might as well not even try.