I also got an 8 in maths at GCSE and upon starting the A level course I was extremely shaky at it. It takes time adjusting to it and you'll likely find yourself having to do more practice to understand and get used to it, it's normal to struggle with it at first even if you did well at GCSE. I didn't really fully grasp everything until year 13, although that's partly because I didn't do any independent work in year 12. I think it's worth continuing the course, especially since it is very valuable as it opens a lot of doors when deciding on a university course.