Hey! I had the exact same thing all throughout year 10/11 (even lower tbh I was getting like level 3s and 4s) but then ended up getting level 7s and 8s in the actual exams all round, so don’t lose hope!
Some tips I’d give you:
For essay subjects like English make STRUCTURES for your answers and try to follow them for each question so you’ll feel less panicked and not waste time.
For subjects like maths you can order maths flash cards online (dependant on your exam board but should be there) and I found them really helpful, also just asking a teacher to take 5 minutes to explain questions or subjects you don’t understand will help and I’m sure they will.
For science subjects I would try and come up with ways to remember things as a lot of it is actually just memory, also a lot of the time gcse science exams have lots of multiple choice a lot of which can be pretty self explanatory, and make up a good percent of the grade.
I wouldn’t worry too much, teachers tend to grade you down anyways.
Hope this helped good luck!