I started the application process with a diagnostic score of like 160V/149Q and ended with 168/160. I used Magoosh and a few practice books. I think Magoosh is like $130 for 6 months or something, and I would really look into that. I hadn’t done much math since high school so I needed something more than just practice problems, and the video lessons on Magoosh were super helpful for me (they also have hundreds of practice problems). This is a much cheaper option and worked well for me.
Also, I just wanted to say that the process for applying to these programs is grueling and often idiosyncratic. I don’t think spending a ton of time reworking your SoP or writing sample now is necessary—just be proud of yourself for putting together a good application and give yourself a break. There’s plenty of time to prepare for next cycle.