What would you recommend I do to become a paramedic/get a medical career

It may be worth having a look at St John's Ambulance cadets

is doing cadets the same as work experience or is it something else? Sorry I don't know much about it

This page explains what cadets are here:
https://www.sja.org.uk/get-involved/young-people/cadets-ages-10-17/

Currently I am a year 12 student with
GCSEs:
Maths, Re : 7
Bio, chem, physics, english lang, english lit : 6
Geography : 5
Computer Science : 4

I'm doing bio, chem, maths for A levels and I am working at grade Ds and Cs currently
I have also completed 20 online medical courses (doing one a day), done CPR classes at school, gotten 2 weeks work experience at a dentistry in a different country, volunteered at my local church for 3 months, going to do work experience ar rolls royce, volunteering at badminton, taekwondo, board game club and charity events at school, completed bronze and silver DofE, and done NCS.

I intend to do some more volunteering, but any recommendations on what else I should do? As you can see my grades aren't the best and I doubt I will be able to do much better than Cs and Ds honestly, Ill be lucky to get Bs I think.

(I also got a diploma in caregiving from the website alison along with my other courses but idk how good of a diploma it is but I thought I would mention it anyway)

Try to get some shadowing experience in a hospital setting in one of the areas you are interested in. Contact your local ambulance trust to see if there are any shadowing opportunities there (this might not be possible if you are under 18).
Also, have a look through this year's paramedic applicants thread to see what shadowing and work/volunteering experience they have:
https://www.thestudentroom.co.uk/showthread.php?t=7393597