Depending entirely on the angle of the shot and a few other factors, you probably did make a good shot if you honestly feel that everything was right. There are certain places and certain angles where, upon exit, an arrow will almost wipe itself clean. If there was blood on your arrow, then I'd be looking for a blood trail, or some sort of indication of exactly where I hit the animal. You aren't wrong by backing out if you think you made a questionable shot.... but I'd get back out and follow up.