If it means anything, in 2014 I took my Additional Science and Core Science exams, got 2 A*s. At AS level I took Mathematics, Further Mathematics, Physics and Chemistry - and got As in all of them. Currently taking FM, Maths and Physics to A2. I didn't feel I was behind any of the triple science students; maybe in a couple of topics, but within the 50 minute lesson I felt completely caught up.
If you can't change, don't worry about it at all!