You need to remove half the difference between the right and left distances from the left hand side and add it to the right hand side. Don't just add spacers to one side without removing from the other and don't pull at the fork links, if there's a gap then fill it not close it.
Can you show a pic with that nut removed? Should it have that nut on? Is there a recess underneath where a disc hub spindle would fit? Failing that, I may have a ScootRS replacement plate that doesn't use the half nut but you'll need a new disc type spindle aswell.