i had this problem for awhile, but just the opposite, i couldnt get it to fit in the screen(too wide),, what i found was a simple adjuster on the bottom board and carefully adjusted that by turning it the direction nessacary,, i had a mirror on the other side to see what was going on with the screen.
-assuming its the vision pro 27",...in your manual, go to page 8..its in the bottom pic labeled sub H size(VR402)... really simple to do.