Assuming this is an hour of homework for this class then it should be enough work. I’m not clear from what you’ve written if you are solving problems without referring to your notes and without using answers or explanations you saw a few minutes earlier. This could be the difference between the tests (closed book) and doing the homework. If you just looked something up in your notes or watched it on Khan Academy then it is fresh in your mind and is one particular point; when you do practice problems it isn’t too hard. The quiz and test are on many topics and its been hours or a nite since you reviewed the material. If it wasn’t really cemented in your mind then you find you can’t apply it as well as you could on the homework. I suggest doing practice problems without reviewing your notes or the book or Khan Academy. You can find practice problems in your book, and more in https://www.amazon.com/Algebra-Trigonometry-Problem-Solvers-Solution/dp/0878915087
As for studying for tests and quizes, daily or almost daily study is better than massed study like you’re doing the 2 days before. The problem with studying the day or two before the test is you read thru it a few times and it all looks very familiar, but this confuses recognition with recall. Second, reviewing itself is not an effective practice. Studies show that self-testing is much better than reviewing. Stop reviewing and spend the time on doing practice problems from the book mentioned above and thinking about why the approach you use for the problem works. Sometimes a student mechanically applies a series of steps from an example to a new problem; the values change so they just crank away but nothing really sticks; they aren’t learning. Read the story of a TA who forced students to rehearse in [Teaching linear algebra](Random Observations: Teaching linear algebra) and you’ll see what I mean here. Cal Newport has written several books for students on learning and he writes about how to do well in a math class at http://www.calnewport.com/blog/2008/11/14/how-to-ace-calculus-the-art-of-doing-well-in-technical-courses/
There is a book I recommend you read this summer about learning called “Make it Stick”. It talks about what works best and has lots of tips for HS and college students.
I agree with previous posters, take this class again next year. Trying to push thru this summer to stay on a self-imposed schedule will hurt you more, given your goals of medicine, in the long run.