Hey, this is so weird but I'm in the exact same situation as you lol.
I wanted to take chem with bio and psychology as well but i'm really bad at maths as well, my college is asking for a 6 in maths for chem a lvl too. i'm not gonna take chem anymore tho coz i've heard that theres a lot of maths in it which i really want to be done with by i get to college lol. i'm actually homeschooled since year 11 so i had the choice to do higher maths.
I don't want to assume i know how good you are at maths because you could easily be better than me, but the chem maths requirements for grade 6 is only the minimum and it'll still be a big jump from the maths in chem gcse and maths in chem a level. Thats what my college told me anyway, and thats why i kinda stopped considering chem. if i was you tho, i would ask teachers at your school if you could maybe resit the mock or basically try to convince them to move you to higher.
If that doesn't work, i've heard that some colleges are quite lenient with requirements, if you explain your situation to them and really prove that you want to take chem, they could accept you.
I had this same problem, i was worried because i want to go into medicine (well more psychology) and taking chem a lvl is definitely a good look when you apply. But it's important for you to know that unis consider psychology to be a science too, and for most unis, i think you only need 2 sciences (unless you're really aiming big).
Also to get into most unis, you don't need any higher than a grade 4/5 in maths and english lang gcse to get into the course.
Please dont stress, there are sooo many options these days that you're always going to have a chance to get a career based in medicine. Even if you end up not being able to apply for chem a level i'm sure you'll have many options. For me, instead of chem i'm gonna prob gonna go with either health and social, criminology or sociology as a 3rd a level.
I'm really sympathising with you coz i know exactly how you feel, but seriously don't worry, gcses are just a tiny part of what you're achieving, esp if you're planning to study medicine.
I wish you the bestttt of luck and ask me anything else if you need : )