It is easy to score A* in any exam if you are disciplined and consistent with your revision process.
Skim through the syllabus and create a checklist of all the topics you need to cover.
Use a textbook/online notes resource to read on all the topics.
Write down key points from these resources in your notebook.
From your notes, re-write key facts and formulae you need to memorize on flashcards and read them daily.
Solve as many past papers as you can.
As you solve multiple past papers, you'll start to identify your strengths and weaknesses. Don't run away from your weaknesses, double down on them till you become good at it, which you will. Do this till you tackle all your weak spots.
Feel free to send me a DM if you need more help.
All the best!