Cutting out electrical boxes may seem fairly straightforward, but overcuts can occur. If you are replacing an electrical box, and the drywall hole is too large for the new box, you can follow these same directions.
If you have overcut a drywall hole (Image 1), you will need to fill in the hole before finishing.
The first step is to measure a piece of mesh tape to fit over the hole (Image 2).
Using a knife, trim the mesh tape to the appropriate length (Image 3).
Apply joint compound to the mesh tape. The joint compound should fill all of the holes in the tape (Image 4).
Cover the area completely with the joint compound (Image 5). Let dry.
Apply a second coat to the area and feather into the wall. Let dry and sand smooth (Image 6).