Obviously we have all said to enjoy college. They really are the best years of your life. The experiences, the friends, and the opportunity are truly unforgettable. Other than the wonderful years of college, let's say you DID get in after 2 years of pre-dent requisites. First of all, in case no one wondered, 2 years isn't that much time (relative to your professional career) to realize whether or not your passion lies in the field of dentistry. Second, pre-reqs are just that, pre-reqs. They aren't very advanced and don't give you near the depth and detail in order to set a solid foundation of concepts of anatomy, physio, and pharmacologic mechanisms. Even though you'll take these upper level-type courses in dental school, after just taking organic and general biology you will surely be in for a rude awakening. Stress will mount up fast.
Point is, I've heard a handful of stories with so-called "pre-req" kids who maintained excellent numbers while in undergrad, but had no prior knowledge in the advanced sciences. Once you take these upper-level, supplemental courses in undergrad, it'll make the dental school ride a little more feasible. If you've only taken pre-reqs, well then you better buckle up.