Like Orims said, it's definitely true that undergrad research research will not determine your field for graduate school. Like you I was pre medicine until a year and a half ago when I started being involved in research. Not only that, but my research was applied analytical chemistry. After determining that graduate school was more in my taste, I worked hard in the lab that I had already developed a good working relationship and was able to get a first author paper, an honors thesis, and several regional presentations out of it. Although my interest was in translational aspects of genetics/genomics and my research background was in soil science (and to top it off I stayed in my pre medicine program!), I had two interviews (I declined Emory's GMB) and was accepted into the University of Utah's MB program which I will be attending this year.
My best advice is to pursue what interests you the most, but I would suggest staying in the lab you are at now if you can see yourself making good progress over the next couple years. Are you allowed a great deal of autonomy, do you lead projects or assist in authoring of papers? If you feel that you can demonstrate interest without having the experience ( via personal statement), but show you have the generalities of research solidified - I say stay. If the lab doesn't offer you either , that is the experience or interest you need, and you feel you can accomplish more at a lab that interests you more - by all means you should make the jump!