Others have already addressed the need for a paradigm shift in the way you’re thinking about this, so I won’t do that. What I can do is cover what it would take to actually accomplish this.

I was a similar kind of student when I was in high school. I never studied and I never got past algebra 1. A few years ago (I’m in my 30s) I finally got fed up with my lack of math skills and decided to do something about it. I had an explicit goal: to understand Calculus.

I went on Khan Academy and started from literal scratch, 1 + 1 = 2. I did every exercise and took every test, making sure I fully understood every concept. Once I got to algebra 1 I started watching every single video as well. I did that for every course up to Calculus 1. Algebra 1, geometry, algebra 2, trigonometry, pre-calculus, and finally calculus 1.

All told it took me about 3 months from start to finish (completing Calculus 1). For algebra 1 to trigonometry (because you said you wanted to be able to take pre-calc), that took me about a month to a month and a half, so I know that that time frame is doable *with the right mindset*. Now here’s the kicker. I was pretty much spending 5 to 6 hours *every single day* on this during that time. Do you have the kind of drive, determination, and focus it will take to do that? If so, I think you can accomplish your goal.

And to prove that what I did works, and is worth your time, after those 3 months I took an actual Calculus 1 class at my local college and got an A. Just make sure that you’re taking the time to understand every concept, because up until Calculus at least, everything builds on top of the earlier subjects.