Personally, I don't think two classes and a lab is too much - it's actually good to have SOMETHING else to focus on other than MCAT alone. Any more than that does tend to be too much, though, unless you're one of those people who "needs" to be busy. It also depends on your timeline! Since the current semester is basically over, I assume you're either thinking about a summer semester or a later one, like the fall. In that case, you have time! Why don't you start reviewing some of the less strategy-intensive material early, like the psych terms? The more of the content you expose yourself to early, the more targeted your passage practice can be during the actual semester.
That brings me to the most important thing to do when taking classes and MCAT - be efficient! I'd advise either a prep course or talking with a friend who's taken the MCAT before (bonus if you know anyone taking the new MCAT before you). Basically, you should have plenty of time to study for the test as long as you spend that time in a useful way, and that involves knowing what topics are higher-yield than others. You don't want to spend a month learning organic chem mechanisms, for example - but it can be easy to get stuck in a tailspin of "too much detail" when you're simultaneously taking classes that DO test this detail. You also want to deeply analyze any practice that you do work through - anyone can find an hour or two every day of free time, even with classes, and it's so much better to DEEPLY analyze a few verbal passages than to try and complete, for example, an entire book without really looking at your mistakes.
Good luck!
