Studying math 8 hours

Basically, what happened to me is that I almost failed math. My passing grade is 75 and the failing grade is 74, and I got 77. This happened because I got lazy and just slept in class while our teacher was teaching. The topic was about precalculus in the first semester. I enjoy math, and I'm strong at recognizing patterns and memorizing information. I'm planning to study for 8 to 15 hours just to level up my foundation. What should I use besides Khan Academy?