The only way you can improve is if you consistently work and challenge yourself. Get comfortable with the feeling of discomfort. By which I mean, do past paper questions in the topics you struggle the most in, check your answers, try your best to figure out where you went wrong. If you are not able to figure it out, attend your school's allocated revision/support session for that subject or approach your teacher about it. Another thing you can do is work collaboratively with other students and see their perspective on how they go about answering/solving problems - I find this particularly useful, because they have the same amount of knowledge as you do.