i think if you're planning on applying to very prestigious universities then it may harm your chances, as they'll have students studying chemistry and maths and doing well up against you who will look better. however, as long as you get good grades in all of them i don't believe it should stop you from going to a good uni - a girl i dance with got AABD at as level and applied to unis to do bio and got 5 offers back !!!! and the D was in biology... so don't worry too much, unless you're planning on going to oxbridge.