Oh I did the same thing the other day with one of mine. It just got away from me, and before I knew where I was there were so many layers that it was just a blobby mess. So I scraped all the paint off his face and started again. It was demoralising as the good bits went west with the bad (throwing the baby out with the bathwater, as it were), but it seemed the only way to get back on track.
Still haven't finished him. Redone the eyes and the bulk of the face, but not the highlights yet. That's where I went wrong before and I'm a bit nervous of it.