You are not moving your knees at all. You need to push your knees forward (at the same time as you break your hips) and get them out over your toes. You are off balance and squatting on your heels b/c you are holding your knees back. Don't look straight down, look at a spot on the floor 3-5 feet in front of you. You are squatting about 2 inches too high (which will likely fix itself when you fix your knees and you can remained more balanced).