I would also suggest taking the August MCAT unless you're applying (in the US) the same year you're taking it.
Anyway, I'll tell you how I studied. Here's some background info: I'm a chemistry major at a small, "not well known for it's science program" university in Canada (reputation doesn't matter much here). I just took the Aug MCAT after my second year. I had finished intro bio, gen chem, physics (all first year), a year of physiology, one semester of cell bio, and organic I and II. So I don't think you need a whole bunch of upper level sciences courses to do well no the MCAT. I did very well in all my courses, so I had a pretty strong science background heading into the test.
This summer I did organic research full time (min 40hrs per week). Working full time and studying for the MCAT did not make for a very enjoyable summer, but it was definitely worth it
I studied using PR hyperlearning materials bought off ebay, I wrote AAMC I and III-V, I also used the big red Kaplan book and the thinner red Kaplan workbook that I bought at a bookstore. I studied a little bit in May, but I didn't actually start to get into it hard core until about the middle of June. Then I tried to study about 2-3 hours a few nights a week after work and then a little bit on Sat and all day Sunday. I had a week off in July and the week off before the test. Those weeks were basically totally devoted to the MCAT. I reviewed the sciences with the PR and Kaplan review books and then did a TON of passages and all the section tests and full lengths that I could.
I think the key is to doing as many passages and practice tests (under test day conditions) as you can. Otherwise, you won't know what the test is really like.
I felt really good coming out of the exam and I got my scores yesterday (11VR, 12PS, 13BS, Q). So, you can definitely do well without doing a course or anything if you can get motivated to study.
Good luck!!