I'm usually a lurker here, and I signed up just to give you my two cents. First off, look deep inside and make sure that this is what you want to do and give it your best shot. Otherwise, don't waste your time losing on potential income. I graduated from a top university with a horrible GPA (sub 2.5), not due to a lack of effort, but due to some personal issues. After I graduated, I started working in research but kept volunteering at a clinic. Once I made up my mind that dentistry was for me, I quit my job, sold my car, and moved to Los Angeles to pursue an informal postbac. I actually applied for a second bachelors so that I could receive financial aid, but my acceptance was denied due to my low gpa. I petitioned for a review and had to persuade an academic committee that my crappy GPA did not reflect on my true academic abilities. I was accepted, and it took me a little more than two years (full-time) to put a dent on my GPA. I repeated some pre-reqs and took as many upper division courses as I could. I also made an effort to get to know my proffessors. Long story short, my "postbac" GPA was a 3.7 and I ended up with a ~3.0 overall.
I am grateful for getting accepted to dental school on my first try, and I really hope that you realize that it is an uphill battle. I may not be the perfect candidate, as many others on this site are, but I think my perseverance and maturity (I'm old) paid off.
I don't think a couple of classes are going to help you out. You have to really sacrifice and take as many classes as you can. Remember, you are trying to show that you can handle a full course load and that you are better than a 2.7. Once you finish that part of your journey, you'll look back and be proud of what you have accomplished. Not only will that be a great feeling, but it will help out in writing your personal statement and give you plenty of confidence during your interviews. Best of luck to you. PM me if you have any questions.