Taking A-Level Chem in a gap year to give myself an advantage?

Right now, I'm interested in going to Uni and getting a degree in Biomed but my predicted grades haven't been brilliant, so I'll be taking a gap year anyways. My current A-Level subjects are Biology, Comp. Sci, and Maths with an EPQ in Biology going on rn but a lot of the universities I was looking at which had coursework I actually enjoyed require A-Level Chemistry in some capacity, usually around an A or a B.

Because of this, I was thinking that maybe it'd be a smart decision to do an A-Level Chemistry exam in my gap year, get the results, and then apply so I can both apply to more universities, use my better grades, and in general just strengthen my application with the time I have.

Is this a smart decision? Can I actually teach myself A-Level Chemistry in that year/is it even worth trying? I won't exactly be doing a whole lot else during that year other than working/getting work experience and trying to flesh out my application so I do have a lot of free time for this.