Shove your knees out hard during the entire rep. Get weightlifting shoes. Take video from a 45 degree angle next time instead of straight on from the back. Otherwise, these don't look too bad.
Embrace the weight feeling heavy on your back. It will soon enough. You won't believe you can squat down and stand back up with it, workout after workout. But you can. You're not afraid any more. You have decided to be strong, and that means pushing your body beyond what you believe it can do. Eat. Eat Eat Eat Eat Eat. Eat.