So basically there is a metal box inside the wall that houses the plug, turn off the breaker, remove plug. Look and see if you can tell how the metal box is attached, you may be able to move that internal box back, allowing the plate to sit flush.

Alternatively, cut a thin wood board for the size of the hole and try to make the wood look normal to the eye with the plug. Then remove the plug, glue wood frame to the wall, reinstall plug.