[Everything up until senior year] Prepping for the SAT's and college math after not understanding math for my entire life.

What I've been doing is I'm starting on Khan Academy 4th grade and going through literally everything. Of course skipping what I know which is the majority of the 4th grade stuff thankfully. I'm planning on taking something in the engineering or science field when I'm in college. So I NEED to get my shit together in math. Like it's extremely important to my future and I need to do it within the next 3 months. Is my idea good?

I can see myself finishing all of 4th through Alg 1 in around 15 hours. Alg 1 and Alg 2 will take around 150 hours or so I bet.

The difference between my skill in math now and when school started is absolutely massive, but I need to still improve a lot. I went through all of Alg 1 and Alg 2 with D's in middle school and 9th grade. 10th grade I started getting my shit together and I'm now in 11th.