Anyone in grad school have advice

So I'm an undergrad student now and I get average grades. I pass and study sooo sooo sooo much way more than anyone else and I never do amazing. I am starting grad school next year which has science based courses/health classes and terrified. I'm passing my classes cause of extra credit and hate doing bad. I honestly feel like I have a mental block that is stopping me from remembering info. I have strong study skills make flash cards have people test me and all but legit the test questions are so hard. Does anyone have any advice? I'm honestly terrified of failing out since you have to have above b averages and I get c's now. I meet with my professors and pay attention in class. I don't have issues focusing but feel like it's so hard for me to remember this info. Idk if it's just cause it doesn't interest me and I'm talking pointlsss classes but I'm struggling and so cared for grad school!!