Leviton Wallplate does not fit standard electrical box
You don't screw a wall plate into the J-box (with the exception of blank plates). You screw it into the device that's mounted inside the box, and that device will have standard holes at the measurements you made. So if you have a GFCI outlet in there, the GFCI will be screwed into the J-box and then the wall plate is screwed into the GFCI.