This will keep you from having to start completely over if things begin to get away from you. You can delete the new Ellipse, duplicate the previous one again and go on. Don't be afraid to go back a ways, if things go awry. This has the advantage of showing you where the natural shadows and highlights are going to be as you create your face. Be sure to convert the path to an image before editing begins or it doesn't work.
Nature is a stickler for balance and the face is a perfect example.
Next, divide the oval approximately in half along the horizontal plane. Divide the lower portion in half again to roughly define the end of the nose. Divide the remaining lower area in half again to give you the placement of the lips. These lines will be smudged away as we work but keep them fairly light to make getting rid of them easier. Now begin adding in the basic landmarks using the airbrush.