I’m not the best person to ask because its been years since I applied to undergraduate university. You definitely need really high marks (A’s and B’s) and some sciences and maths and english. This is a good question for your teachers and parents as they know you better than I do. I would find out what grades you need to study medicine at university then speak to your teachers and tell them what you want to do, they will be able to help you and tell you what exams to take etc
Good luck with it all and I hope you get to study medicine 🙂
As Vicky says, the important subjects are going to be science (you’ll need at least two I think, or double science) english and maths. Good luck, it’s a lot of work but if it’s what you want to do then go for it!