"Sitting back" depends on the style of squat you want to do. Sitting down like you are in the video is fine, you just need to make sure other things are taken care of.
You are not in ANY way tight enough. Your whole body from the soles of your feet to your upper back and traps should be squeezed as hard as humanly possible (this means no breathing during the motion, only in between reps when you are standing). Loose body translates to power loss and increased risk of injury--although I don't think your form looks particularly injurious.
I would slow down your descent a bit. Note--I don't mean super slow, I mean about 25% slower than right now. There is no special purpose to this other than to get you FEELING the motion and staying tight as humanly possible as opposed to just flopping down.
Work on some mobility for your legs (both ankles and your hips). When you descend the weight transfers to the inside of your footstep. This should not happen. You can see it in the way your feet lean inwards on subsequent reps.
What part of your legs do you feel working the most when you squat?
Do this mobility drill to modify your squat form: find a solid upright object to grab onto--an upright of a squat rack works if you have one, I couldn't see from the video if you had moveable stands or a rack. So find an upright pole, hold onto it in both hands with your feet about hip width apart and toes pointed almost straight forward (they don't need to be perfectly straight, just close to it...straighter than in the video you linked). Then using your hands to balance yourself so you don't tip backwards, squat down slowly to the bottom of the squat position.
Your toes should remain where they start without turning out any additional amount. At the bottom your arms should be inside your knees and your back should be straight.
If you can't keep your heels on the ground you have ankle flexibility issues. Work on them and they will go away, including just stretching calves in between sets of squats.
This is the pole squat:
but I dislike her toes being pointed out that much. When working on mobility with hands to keep you from tipping you should work on straightening the feet out some.
This is a good position from the front:
Notice the toes are mostly forward not out to the side, the knees are slightly wider than the feet. This is a slightly exaggerated position for the use of stretching and teaching mind you.