Don't worry about not taking the labs.
The classes of a prep course aren't really necessary. However, the materials you would have available to you(ie practice tests, review books, etc.) are very valuable. They will help focus and streamline what you will be studying. (Rather than flipping through old books that go into much more detail than is necessary for the mcat) If you don't purchase the Kaplan materials, make sure you purchase another company's review materials or examkracker books or something. They will help you immensely because they focus only on the topics that will be on the test and only go into the level of detail necessary for the test.
The classes however, are worthless. Your time is better spent reviewing the materials on your own. Usually the time you put into studying and practicing on your own will determine how well you do on the test.