My husband says:

You need to remove the screws holding the outlet in the wall (turn off the circuit breaker first) and place spacers between the butterfly part of the outlet and the wall. Reinsert the screws and tighten until the butterflies are flush with the tile surface, I purchased the plastic spacers at Home Depot in the electrical department.

Thanks, I'm glad to know there is such a thing as a spacer for the outlet. That will make my life easier, nuff stress already installing this backsplash. 4" tiles on the diagonal. But so far, so good, and it's going to look great.