Chertie, looks like tour making progress. The one piece of advice I can give you to go along with watching your center line is to look for ridges to run your flakes on. The ridges are usually on your thick spots anyway and if the ridge runs across the point then the chances are good that the flake will run past the center of the piece. Also be patient and grind your edges. Look at your point from all angles before deciding on where you need to take your next flake. One more thing that really helped me was to attend a knap in. There is nothing like seeing it done in person by people who can explain how to do it.