I think im gonna have to repeat a year in high school... what should i do?

Well if its the teachers fault its likely everyone will do badly. Howe do you know you made mistakes if you havent had your results uet? If you know you are weak in a subject then you have to study more on that subject than on others. If you think the teacher is not good enough then have some private tuition. If all the kids are struggling then maybe a few of you could get together and share a teacher.