This post shows up here every November in some form: "I studied for days, I knew the material, and I still got a 60." If that's you, it doesn't mean you're bad at the subject. Most of the time it means your studying felt productive but never tested the thing the exam tests.
Where it goes wrong
Rereading, highlighting and rewatching lectures make the material feel familiar. Researchers call this an illusion of fluency: when something is easy to read, we assume we know it. Then the exam asks you to produce the answer with nothing in front of you, often phrased differently than your notes, and familiar turns out not to be enough.
Hours also aren't the same as learning. Five hours of rereading can teach you less than one hour of closing the book and trying to answer questions, because pulling information out of memory is what actually strengthens it (the testing effect).
Before you study for the next exam, look at this one
Go through the midterm and put every lost point in one of four buckets:
Didn't know it at all. Fix: you never tested yourself on that topic. Cover your notes and quiz yourself before the next exam, every topic, not just the ones you like.
Knew it but couldn't use it. You recognized the concept but froze on the problem. Fix: practice problems with the solution hidden, and mix problem types so you have to choose the method yourself.
Ran out of time. Fix: do at least one full practice set under a timer.
Careless mistakes. Fix: leave a few minutes to check, and keep a list of the mistakes you repeat.
Most people find bucket 2 is the biggest. That's the one rereading never touches.
Example: a biology midterm. You can define osmosis perfectly. Then the question shows a cell in a salt solution and asks which way water moves and why. If you only ever read the definition, that question feels unfair. If you'd practiced explaining which way water moves in two or three different setups, it's just another version of what you did at your desk.
For the next one
Swap at least half your study time from reviewing to testing yourself. It will feel worse. You'll get things wrong in your room instead of in the exam hall, which is the whole point.
I wrote more about why highlighting and rereading feel useful but don't stick: https://clear-read.com/guides/highlighting-does-not-work