Use a brush slightly bigger than the target spot.
The Healing Brush
The Healing Brush tool, located under the Spot Healing Brush tool, is very
similar to the Clone Stamp tool. To begin, Option + click (Alt + click on a
PC) to select your source, and then carefully paint over the destination to
transfer the pixels. The Healing Brush performs this operation with more
built-in intelligence than the Clone Stamp.
As with the Spot Healing Brush, the Healing Brush attempts to
automatically blend in the cloned pixels with the environment around it.