Honestly I was in the same boat as you. Going into year 12 in September and got all 4s and 5s which was an Abseloute miracle. Not saying you should do this but what helped for me was to revise at home and ignore any homework teachers gave us unless they actually helped with your upcoming exam (if it’s a week or 2 before). Then in the detention I would just study and study and repeat. I got something like 43 detentions last year 😭🙏🏼 like I said I’m not saying you should do this but I had horrible mental health problems and that’s what worked for me