Bought a droid on ebay but I dont want it?

I recently purchased a verizon droid on ebay. It seemed like a good deal until I saw I could get a cheaper pre owned one from verizon which would include a warranty. I decided to just upgrade instead, but in the mean time, the droid I paid for on ebay hasnt been shipped yet. It has been 4 days. Is there a possibility that I can contact the seller and ask them to cancel my transaction? If so how do I do it? Im sort of new to ebay.