Agree with Mark on the leaning back a bit. I am one to know about this one....I was a "leaner" back in my early swinging days. To fix this there are three things you can do:
1. Imagine there is a wall behind you on the upswing. Keep the back straight and picture pushing your head up through the ceiling.
2. Planks, planks, planks. If you can get the proper tension right with the plank, you will notice that it will feel more solid at the top of your swing.
3. It's hard to see in video, but make sure to tense the glutes at the top and also pull the kneecaps up. This will help with the proper snap at top of swing and make your "float" a little quicker too with the bell
Hope that helps