You see a lot of advice here on taking classes over again, taking lots of classes to raise your GPA, etc. etc. etc. My situation was a bit different, but here's what I did:
I went to school first 20 years ago, went for 4 semesters but basically failed every class my last semester because I didn't go. I withdrew myself because I just didn't know what the h*LL I was doing. When I went back to school, rather than take just 1 or 2 classes a semester, I took 21 credits. And 12 credits in the summer. My major was/is math, and I fell into a chemistry double-major along the way. So, in three years, I've taken 120 credits of extremely difficult science classes and done very well.
Overall, my GPA on AMCAS looks like crap because of my mess 20 years ago. However, I have gotten lots of secondaries, only two rejections (so far), and even a screened secondary invite. (BTW, I took the April MCAT and then retook in August. Still waiting for those scores). What I do have going for me is a TON of medical experience and a VERY long history of going above and beyond to volunteer in the medical field. All before medical school was a star in my sky.
Basically, you have to now prove this is what you want. Show your devotion, buckle down and get stinkin' awesome grades and a really good MCAT score. Advice I got early on was to take a load of classes that were difficult to prove I could handle the workload. Talk to some nearby medical school admissions offices and get advice.
Above all else, if you go back to school, get another degree in something you LOVE to do. DO NOT... repeat.. DO NOT do Biology just because some idiot in the pre-med office told you that's the degree you have to have for med school. Heck, major in art history if that floats your boat. Just get good grades in your pre-reqs while you do it.
Good luck!!!!!