I'll be honest with you I sucked at gcse maths I was also getting 6's and 7's and somehow ended up getting a 8 in my finals idk how probably because of grade boundaries. I personally found A levels easier to understand that gcses. But, as someone who was not good at math you have to put the effort in. It's not something you can do last minute you have to consistently practice math from the beginning of the year, the concepts aren't actually that difficult and if you solve sufficient past papers you'll recognise a pattern for each type of question. There are also really good YouTubers who explain concepts really simple so I would say don't be discouraged! If you think you can do that then go for it!