I can say just because you fail at A Level doesn't mean it's the end of the world.
I ROYALLY messed up my A Levels (Biology, Chemistry and Maths) and my only full A Level grade I took to completion was Biology (I got a D), in Maths and Chem, I got two Us.
I took a Foundation year at uni before moving onto Biomedical Science at UWE and graduated with a 2.1. After this, I went on to do a teaching course (and very quickly left, all I can say is, stay away from Brighton Uni, it's a terrible course). After that, the plague hit, got a job as a medical lab assistant before being promoted to an associate practitioner after 3 months.
Worked as an AP for 3 years before deciding that I need a Masters (Biomedical Science but specialising in Clinical Biochemistry) to get ahead for the higher jobs. So I'm doing that right now and have been getting consistent 67-70% in all my work (minus two pieces which are heavily med micro based (still passed them though and very small pieces which won't count to my final classification), I hate micro, I'm a clinical biochemist and not much else).
So, even if you mess up A Level chem, don't worry about it. There are plenty of options.