hii!! thank you so much!! i believe that with the right methods and amount of focus on each area, you'll be able to achieve great things. i went from roughly 7-6 in science in year 10 to a 9-9 in my gcse's.
at year 11, i did get overall 9's in my mocks, but this was mainly because i went through most of the maths past papers in my year 10 summer holidays, so i had a lot of experience. i would get 9's on two papers, and an 8 on one paper, which is exactly what happened this year! i definitely believe that going from a 6/7 to an 8/9 will be a lot easier with the right mindset and revision strategies.
maths is all about practising a wide range of past papers / exam questions to explore the potential scenarios for certanin topics that your examboard could include when creating the current year's papers. it is crucial to become familiar with the phrasing and formatting of worded problems so that the language doesn't stump you during your mocks / gcse's. i would always practice a past paper, mark it afterwards, and then look up a walkthrough on youtube for the exact paper to see how to complete any questions that i got wrong. i would further advise watching videos and practising quesitons on the topics themselves so that it becomes a more familiar, comfortable concept in your mind.
personally, i believe that the differnece between those who get 6's - 7's and those who get 8's - 9's is the amount of practice they do of worded exam questions as well as the ability to adapt and remain calm when seeing an unfamiliar question. students can be extremely prone to exam stress, not just during the spring / start of summer, but throughout the entire year. learning to control these emotions can be very useful; especially in an exam. during my second gcse maths paper, there was a 7 marker - 7 markers hadn't appeared in ocr for a few years - so, naturally, i was quite stumped, however, remaining calm and level-headed really helped me work with the information i had been given and eventually get to the right answer. i believe that if i hadn't followed my own advice and allowed myself to panic during my exams, i would have gotten an overall 8 (which is obviously still amazing, but i just wanted a 9).
my personal advice would be going into the exam
knowing that there'll be a few questions that seem odd, or are worded strangely at first - it can be very daunting if you try to convince yourself that you know what to expect based off of teacher's predictions or past papers only to realise that there's a 5 marker that looks completely different to any other question you've completed before. keep calm and
look at what you've been given, as well as look at what the question is asking for. are there any shapes you know certain formulae of? is it possible to work out any missing lengths? can trigonometry be used? what potential topics could be relevant to the method needed to work out the answer?
tl;dr: yes, i do believe you can stretch to get 8's / 9's with the right amount of practice and familiarity with the topics in your examboard.
maths channels i recommend would be The GCSE Maths Tutor, 1st Class Maths and CorbettMaths. there are many other amazing channels for gcse maths too though, so feel free to check them out!
i was pretty all over the place with my revision. i would usually try to fit in an hour of revision per day on at least one subject, whether that be making resources, practising past papers or going through my flashcards. i recall in one month - perhaps april - i did around 60+ hours of revision after the whole month, so roughly around 15 hours per week (however, my time was very unbalanced; i did procrastinate for quite a while at some point, so i ended up doing more revision at home on some days than others). it was definitely quite a struggle to fit all these subjects in... i didn't revise physics 2 until the week of the exam! but i think making a revision timetable would make it easier for yourself.
an 8-9 / 9-8 is the same thing im combined science - they just write the higher grade first. if it helps, this year, the difference between an 8-8 and a 9-8 this year was 19 marks (251 to 270). bear in mind that it's roughly 70% in each paper for a grade 9 (roughly 49 marks, give or take), however, there may be cases where grade boundaries are lower / higher in some papers (e.g. it was 44/70 for a grade 9 in chem 1 this year, and 51/70 for a grade 9 in physics 1).
i hope this helps!!