Instead of just reading text books and trying to memorise facts by rote, try reading some paperbacks written for the general public. It might help concepts click better, then you have a more solid foundation to build on.
Example. I 'knew' thermodynamics. Could use and work with the equations. But I didn't really 'understand' the subject until i read 'Four laws that drive the universe' by the brilliant teacher Peter Atkins.
Alternatively, ask a few universities if thety wouldn't mind providing you witha list of recommended reading for year one B.Sc chemistry. Can usually pick an older edition second hand for next to nothing from places like Amazon. If you are comfortable with even half of it, you'd do exceptionally well at A-level.