You don't have to exaggerate the "pinching" of your shoulder blades that much. Just get into a good, tight, position that isn't too rounded, brace well and keep the brace. You don't have to arch that much in your lower back at the top either, it looks like you are not using your ass enough to push the hips through.
Again, these things are hard to say exactly. We all have different bodies and our technique will vary. Whatever your optimal form is, form breakdown and losing tightness will be a clue that something is weak in the chain or should be worked on. As the other guys said, 1. touch the ground, 2. secure the weights, 3. post a video of something a little more challenging.
Remember, it's a skill as well. Shit takes time.