How do you prep for a open note math exam?

I’m currently taking elementary algebra. Our teacher allows a page of notes for the exams but the exams are still very hard. She tells us the best way to prep for the exams is to get perfect scores on our quizzes and study them (we use mymathlab) before hand. What I’m doing to prep is that I write down the problems and the steps of them from the quizzes that I don’t understand because I’m thinking they will be the same problems but with different numbers but this is not the case. The problems are extremely tricky. Please someone help me! This is the 2nd time me taking this class and I can’t afford to fail it again. My last algebra teacher allowed a page of notes too but also made the tests the same way. Why do teachers make open book/note exams so hard anyway?? I’m getting to the point where I just care about getting a C so I can move on to the next math class. I know once I learn how to prep for open note exams, I’ll be fine from here. Thanks for your help everyone!