Hey Andrew
You're not really getting your back set here and you need to be more patient with Step 4™. You need a lot more squeeze up of the chest and you're trying to get the back flat. At least, that's the mental picture you need to have in your head. Lift the chest in an attempt to point it at the wall in front of you and think about using the barbell to pull your belly to the floor. Your low back is really what we'd like to prioritize, but setting the thoracic spine properly seems to help with this.
There's a few videos on the YouTube channel that may be helpful.
Also, rock back off your toes on the setup before you go to set the back. You're a bit forward of midfoot.
Hope that helps.