Used circle cutter in wrong place in drywall, best repair method?
Cut some short strips of plywood or even paneling (long enough to overlap both sides of the hole by a couple of inches). Don't cut your fingers off.

Put the plywood strip(s) in the hole and position the strip so it is extending out beyond both edges of the hole, behind the sheetrock.

Hold the strip tightly by pulling outward on the back of strip with your fingers, and drive  screws through the sheetrock and through the plywood strips.

Now, put the sheetrock cut-out back in place, and screw it to the plywood strip(s).

Patch the sheetrock.