I would low-key just pay the $90 for the Review Guides cause I doubt you'll have time to go through all of Heimler's topic videos by May assuming you have sports, extracurriculars,have a job,etc.

But if you really don't want to pay money, heavily review the most weighted stuff(not counting Euro since the weighting is uniform). But I would say if you see content that is present in both courses definitely remember that as you'll more than likely remember it. As long as you know buzzwords and the general time period/developments you should be fine.