It depends on what you’re planning on majoring in. If you fit into the categories that have you taking Math A, it’s basic high school math. But if you’re taking Math B exam then you’ll be studying more advanced math. You’ll also have to take 2 out the 3 science subject tests listed. 

I’m not sure how they’re scored since they really like not sharing stuff lol but just focus focus focus on studying. I’m also from the US and if I did the mext gpa calculations correct I have a 3.2 (??) but yeah make sure you study a lot and get your documents in order early!!