Hello and welcome to the community Erstwhile. Glad to see a keen Year 10 student on here.
I do all the questions my teachers give me but I still manage to mess up during exams...
Have you understood the reason for 'messing up' during exams? This could be due to a number of reasons... such as panic or stress out before a high-stakes assessment such as an exam?
I think in mathematics especially, practice is key. Practice leads to confidence, and in a lot of situations, this is the main problem. Mathematics is perceived to be a hard/difficult discipline and attitudes (by self, peers and the people around us) can affect the way we achieve and do maths.
I was never good at maths but I am ready to change that this year,
If you aren't 'good' and still are getting 75-84 in your tests and other assessments, I think this is a good start. It shows that you have a competent level of understanding to expand further. I am using single quotes around key words because these are your words, not mine
Like I said above - I think confidence is the biggest problem for a lot of students in mathematics (through self-doubt and second guessing).
I do all the questions my teachers give me
And what else do you do? The amount of resources for maths topics doesn't stop at the teacher. You are able to independently explore too.
Do you get any sort of feedback from your teachers as to questions you get incorrect and
why? Feedback is an extremely strong tool for building on your existing knowledge. Learning from your mistakes is so important, and you are usually given multiple opportunities to improve (e.g. through a topic test, then an exam... where the topic test would be the first real opportunity for you to understand your misconceptions).
Obviously there are many other solutions and mine is just one, but I think confidence and the use of feedback are two important starting points to your success. Good luck for the rest of the year