Should I move to combined science from separate?

So I am currently in year 11, 16 weeks until my exams, and in Science, especially in my school we are all in a tough situation, in year 9 (first year of the course we had no chemistry teacher all year, no biology teacher for a half a year and had no physics teacher for half a year) so already in year 10 I was very far behind, well the whole class was, year 10 was fine, despite the fact that our physics teacher was really slow at teaching, but now in year 11, our biology teacher and chemistry teacher both went back on maternity leave, from September until January we had no chemistry teacher, and at christmas our physics teacher has just left. So in physics we are extremely far behind and Chemistry, we need to get through about 30 topics in 15 weeks, which we are barely able to scratch the surface on. In my last set of mocks I got an 8 in biology and 5's in the other two, with target grades of 8 in all science's. I also want to study chemistry a-level, I fell right now just dropping to combined science instead of single/separate/triple and getting two grades instead of three will be more beneficial in the long run and I know them grades will be a lot higher, would it be worth it due to how far behind we are?
Sorry for the long post.