First, don't get too stressed. While its important to revise, burning yourself out will only lower grades in the long run. Second make sure to consult your teachers on what you can do to improve your answers (I didn't do edexcel so i can't give relevant tips to what ur doing). Finally, try to do past papers and ask teachers to mark them if possible. I did 1 a month leading up to my exams and did pretty well in my exams. That's the best advice i can give you, recalling from my experience