1366x768 is 720p. Your TV's resolution is 1366x768 not 1280x720 so don't try to force that resolution on it. They are both the same aspect ratio so the image will not be distorted in any way, but running at a non native resolution will impact quality. Your pc is seeing its native resolution so leave it at that.
Confusing I know but check your tv's actual resolution in the manual.