From what I have gathered through applying to Cambridge, the options you choose for GCSE don’t necessarily matter, however grades do sort of, as a lot of the people applying are going to have the best of the best applications. They care more about predicted grades at A level, and the subjects you take then. I applied in October and got rejected sadly, but it was down to the fact I wanted to do a science based degree, with only maths and physics, and no chemistry/ biology. Good luck with it all, and honestly dont stress too much!!!