i was getting Ds too at the end of y12 because i wasn’t naturally gifted at chem. however i started to get more confident in y13 where it all started to tie in and make sense - but i did put a lot of effort into chemistry compared to my other subjects
i managed to creep up to a B and then an A* in my last mock
chemistry is definitely a challenge and requires a lot of effort to be good at it. if you’re really really struggling and have no interest in chemistry, then I think you should consider some alternatives
about the fast track A-level, if you don’t think you’ll be able to cope cramming 2 years of content into 1, then absolutely do not.
don’t worry about falling behind, you can retake year 12 (it’s not the end of the world) and take all the time you need to get really good grades in the subject you choose
if you think you want to carry on, you should talk to your head of year about changing teachers. if their teaching style doesn’t suit you, then it will have a direct impact on how well you do. if you stay quiet then nothing will change (i regret not speaking up lol)
but i really think it’s possible for you to get the grades you want if you put the effort into it, even though it sounds really cliche
at the end of the day it’s up to you!! good luck, hope what i’ve rambled about has been useful to you