Yep, you can’t get behind in math or foreign languages and then cram for the test. Once I learned that, I did OK in college. Never went beyond the first course in differential equations, though that came in handy later when I took a physical chemistry course.
Naturally, I have long since forgotten most of what I learned in college. Sometimes I think about digging out my old calculus textbook and seeing if I can work my way through it again for mental exercise.
I would suggest the website three blue one brown. Really well done videos on different math subjects. I went through their linear algebra classes and it started to make sense. Best of all it is free.