If you want to continue using the corner pin method, make a precomp the same size as your final comp and build your patch there, it should just be the cloned area, no background. It will need to fill the entire comp. So either scale it up, tile it, add some blur. Then drop this precomp into the final comp and apply the mocha corner pin data.
For your particular project, I would probably be using mocha shape tools and mask tools, there are tutorials at mocha that can explain that method.
Johnny Cuevas, Editor
ThinkCK
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.