A/A in double with an A in math is more than enough. Which GCSE science course do you take by the way as in my opinion (as a A-level chemistry teacher) some are better preparation than others.
Sure, at the start you're going to have to work harder than a triple student with the same grades, but that's just because triple has content that is usually taught at A-level, so triple students will have already done some of the early work. There is no prerequisite knowledge that is needed that you don't have.
My school only recently started offering the triple science course, before that all students did double and many of those managed A-level chemistry perfectly well.
The elitism surrounding triple science seems to generate a stigma about double that puts people off doing A-level sciences, which is a shame. My most able yr12 student is a double scientist, and they got 100% in the January AS exam. The work their ass off though.
As a number of posters above have commented, more important is how hard you are prepared to work if you need to. There is no reason why you shouldn't do well at A-level sciences if you're prepared to put the work in.