I am not saying you don't know how to center your bindings, dude
a photo from the top would show us what your angles are and what exactly the situation is. You know, showing context. Just a zoomed in shot of your toes hanging off the edge, is just that. I'm scrolling up and down the page trying to imagine your whole binding.
what's the ww of the board?
No, Burton doesn't have a disc for that. They've got a special disc for side to side adjustment though, but you can't flip it otherwise you lose the reflex flex.
and the medium discs are the same size as the large, so your fundamental problem wouldn't change.
btw do you extend the gas pedal at all?