Extra problems are the cure to your ills. Mastery...
There is a book called Mastery, by George Leonard which speaks to how those who are the very best at what they do are not naturally gifted but rather they work very diligently – repeating their craft so much that it is engrained.
It is the same for math. Don’t just do you assigned homework – do extra problems. Don’t just prepare for the test – find old tests by the same teacher or others and work them in a test-like environment.
When I was in graduate school, there was a statistics class, and for whatever reason I was able to find this professor’s old exams – several of them for every test. In addition to working homework problems etc., before every test, I worked ALL the tests for that topic. I could have gotten an A blindfolded! One time, the test WAS IDENTICAL to a test I practiced EARLIER the same day. It was all I could do to not start laughing. But I felt no guilt - I WAS P-R-E-P-A-R-E-D and worked hard preparing. I was going to get an A no matter what.
An extra book is helping as a source of fresh problems of the same type you need practice. Work the odd problems that have answers in the back.
The internet is a resource too – but be careful as anyone can put stuff out there.
Work extra problems of the same type for which you can check the answer.
Think “mastery”...