They do a breakdown of the subject matter on the GRE page, probability theory is one of a couple of dozen side topics in the 'Additional' section, which is worth 25% of your total score. Given an even distribution, you should assume that there might be at most a couple of probability questions on the test all together. They probably expect minimum competence, I would be surprised if your course isn't good enough presuming it's a basic calculus centered stats course.
That being said, I think probability is pretty interesting and useful (especially for an applied math person, don't know if you're one or not) so I would recommend that you either take an additional course or just self study (I find probability to be pretty fun and intuitive, I don't know if you have the same outlook though).