My experience in the start of year 11 after doing horribly on my first year 11 adv and ext math task was to slow down firstly with trying to do math, so I would take time with my working even if its not 'fast enough for an exam', and try to really understand concepts in maths in my own words than a textbook's, like what do the solutions of a quadratic really mean? Its not the fact we have to fully understand math, but its just thinking about what maths truly means to us.
Another thing I started doing in year 11 was to read more books, especially fiction/fantasy. In my opinion harder questions in mathematics are a product of your effort along your math journey, what you've learnt and retained (especially in geometry based questions), and your imagination. So if you can give your imagination some time to unfold it can do wonders. If your not into books movies, comics, anime, manga, or just going outside and taking a walk in a park gives your imagination a time to unfold. (this is, in this reporter's opinion, how math and english adv --> english and math ext 2 students flourish in both subjects, they found a bridge between both subjects, so they can enjoy and succeed in both subjects).
You mention more practice and of course you need to practice, but once you understand a topic all you can do is just not make any mistakes. 90% of questions in internal tasks are always going to be your textbook homework questions, so just learn not to make mistakes (ik it sounds superficial but still its the root to why we lose marks in tests). If you are really keen then you can do further research on the topic your doing, like with geometry go on its wikipedia page and read about it.
One thing I've seen happen to a lot of people is burn themselves out. It's great your watching Eddie woo and doing online study but talk to yourself and ask yourself if you need to take a break. Especially in stage 6, your mental health must come first. My motive in stage 6 was to have fun (my definition of fun is very weird), and in my opinion I had a lot of fun, without burning myself out.
Another thing is don't compare yourself to others. Of course there are math prodigies in our world but comparing yourself is the thief of happiness. Stay in your own lane in your math journey and you will be fine. Richard Feynman, a world renowned 'math genius' and physicist said he "was an ordinary person who studied hard". What I'm trying to get at is your frustrations are meaningful and heard by many alike but if you find a passion or need for math then it is possible for yourself to get what you want.
In exams I improved my marks by just writing neater. It sounds weird but when I write neater I write slower, so I think more, so I pick up on my mistakes. In tests and high question exams you will start to be on a time constraint, but if you plan out your exam, you can do the harder questions first and move down to the easier questions where you can do those quickly.
Also read your working out like your reading text. Mathematics is said to be a language so if what you write doesn't make sense how would the marker understand it?
Don't get too hung up on formulas too, of course it's important to know before an exam, like simple interest, but a lot of formulas you learn are just given to you, you don't understand how they are derived. Like all volume formulas are derived from volumes of rotation (or cylindrical shells), but you learn that in year 12 of ext1 maths. I would focus more on safeguarding yourself from making mistakes, like double checking your answers, making sure your transcription is good (ie your fours dont look like nines, your fives dont look like an 's', sevens as one, ask your math teacher for tips on that if you want).
Finally, those random/hard questions are the essence of our mathematical ability, in ext 1 and ext 2 they can give us university level questions like proving the infinite series of a number or solve an a5 putnam integral. Rarely they teach us those concepts, its up to us to figure it out. So you just be nice to yourself, there is nothing we can really do if we don't get a question. Write out what you are given in the question, what formula's/concepts apply to the question, and go ham. You should get pity marks at least, but if you don't get the correct answer, the previous questions will be correct if you haven't made mistakes so your overall mark wouldn't hurt.
Hopefully that somewhat helps, I know its a bit unorthodox but it should somewhat make you happier at doing math. I don't like how they teach maths in stage 6 because its heavily reliant on your marks, so it doesn't assess understanding, rather if you can plug numbers in, but then there is the antithesis 'if you know it you should've gotten it right'. And we have no say in how they examine us academically, so play the game, don't make mistakes in exams, and have fun in what the game is about.
If you want some accreditation from me I went from being a low ranked math student into 3rd/2nd in math adv/ext. (there are some massive tryhards in my cohort)
