Study advice?

I’m taking a pretty advanced BIO, and I’m struggling getting test grades above Cs. I’m studying the text, my notes, and using the YouTube. I feel like I have solid understanding of all the concepts but it’s like the test are 30% more in depth than her lectures and 10% more in depth than the textbook. Asking my teacher for advice was useless as she just said “don’t overthink it.” Like, how can I not when your tests are 30 times harder than how you present the material in class? I’m passing the class but want to do better. Advice?