Sam didn't have have a chance to change his mind. He was up on the stage and standing in front of a crowd before he could have blinked twice. He suddenly found that he had stage fright, but he wasn't stable enough to act on it. The booze was starting to kick in from their last drink. So he turned his gaze away from them and looked over at the list.
Dean would have throttled him alive if he sang any of the three.