Hi lsatstudent,
Assuming that you took this CAT in a realistic and test-like fashion, then your initial score is really strong (the average score on the Official GMAT hovers around 540-550 most years). You're clearly a strong critical thinker, so focusing on the Quant section (to learn the necessary content and Tactics) might be what you ultimately need to score at a really high level on the Official GMAT. As such, a full Course might not be what you actually need. Before we can discuss your options going forward, I'd like to know a bit more about your timeline and goals:
1) What is your goal score?
2) When are you planning to take the GMAT?
3) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich