Let me tell you one thing, in GCSE maths you could pretty much memorize a method for almost all types of questions and get a 9 that way. So just because someone got a 9 doesn't necessarily mean they're actually amazing at maths. Of course there'll be some people with 9s who are mathematically gifted but most people and their school just think they're smart in maths when they're not and only do loads of past paper questions, go over the same method multiple times sub-consciously and then regurgitate it in the exam with same recycled style of questions.
So now talking about IB, HL AA is extremely hard even if you were top of your maths class at GCSE. And the reason is because it actually requires intense critical thinking and CONCEPTUAL understanding, which GCSEs just doesn't examine. So no-one aged 15-16 can truly predict how they will handle HL maths regardless of their maths ability. Neither can their teachers. Now obviously I don't know you personally, but there is a chance that you are able to synthesise a method constructing a rational thought process when given a difficult, multi-step problem even if you didn't get a 9 in GCSE.
That's the difference between GCSE/A-Levels and IB. In the former, you are taught to memorise methods to solve a style of question. In IB, you learn to CONSTRUCT a method, because IB is very creative with their style of questions. Many questions are novel and wordy year on year.
If you're good at thinking outside the box and applying concepts, then it's for you. And anyway, you get follow through marks even if you get the answer wrong.
I didn't mean for this to be a philosophical speech or anything (although looking back it kind of is), but to conclude, HL maths is extremely tough and requires a gargantuan amount of hard work and patience to sit down and etch those concepts into your brain so you can apply them to any question, even if you haven't done that style of question before. You getting a 7 in GCSE maths actually tells me very limited info about your true mathematical ability but if you are willing to make a HUGE effort to get so and so grade, then you will!