How can I retain what I actually studied?

Just bombed my calc 1 exam (and the class). This is the second time I've done so. The first time, I had no idea what was going on, but this time was different. During class, I understood how the problems were solved, when doing the practice problems to study for the test, I can solve them, but as soon as I look away from my notes and previously solved problems, sit down for the quiz or test, and try to solve it, I suddenly lose the ability to do so. Is it as simple as just "do a ton of problems until it comes naturally" or is there something I'm missing?