Listen, i am not trying to be a jerk, but i am going to shoot straight with you. If you continue down this path, you have a 0% chance of being a dentist. Even at this rate, you will have to do some serious work to improve you GPA to be competitive. I am not saying finish by getting A's for the rest of your 20 credits....i am saying that you will need to do a lot of post-bac/masters work (especially in the sciences) after that.
Think of it this way... if you take an additional 50 credits and get a straight 4.0, you will raise your GPA to a 3.02. Which is still not competitive, but at least above cutoffs. You will need to take an additional 100 credits of a straight 4.0 to raise it to a somewhat competitive 3.27. Even then, you will need a good DAT score of 20+ to compensate for the GPA. Realize that this will take an additional 3-4 years of work and 3-4 years of more debt and money to go to school. Not to mention, with your current study habits, you may not even be capable of getting a 4.0 for 3-4 years straight.
Then, you need to be prepared after all that work, there is still a chance you don't get in. You need to look deep inside yourself, honestly, and see if you have the will power and work ethic to make this happen. There are still plenty of respectable, good paying careers out there for you, that may be smarter decisions in the end. Good luck!!