Retaking the SAT in College

Has anyone else retaken the SAT in college? I’m currently in college but I’m thinking of transferring to a different school that requires me to have a higher SAT score (I was only off by 20 points!!). I’m not too worried about the English portion but I’m very concerned about the math section since I haven’t taken a math class since I was a junior. I’m going to study a lot to try and remember all the skills I need but I’m not sure where to even start! I basically need to relearn three years of high school math. I’m planning on using Khan Academy since I can’t afford a math/SAT tutor.
If you retook the SAT in college, what helped you study/remember all the skills? Did you improve your score? Are there any good books I should read that will help? Also, what skills/topics (math in particular) should I most focus on?
Thanks!!

I should add that I’m applying to an international school that doesn’t take college credits, so I’d be applying as a first year, hence why I need to retake the SAT