hi, don't take maths if you don't enjoy it. Don't take any subject if you don't enjoy it.
What subjects do you like besides biology and chemistry ?? Your main goal should be to do well in your third a-level and secure an A, so the best way to do that is by choosing something that you find interesting and are therefore able to focus on.
I know quite a lot of people who want to study medicine, and they have a wide variety of third a levels (other than maths). Some include French, Psychology, Philosophy and Ethics (I take this), English lit, Economics etc etc. It's pretty much up to you!
If you are at all thinking about philosophy and ethics/ RS, then I would recommend it- it's a nice change from the sciences and the way I have learnt to write answers, especially to do with ethics, in a certain structure will definitely help me at medicine interviews. And I think maths doesn't massively help with chemistry, as chemistry is often to do with a specific kind of maths/ problem solving that isn't as complex as a-level maths- I am managing very well in chemistry without maths.
Best of luck.