phildflyer

I did a repair job on the underside of my wing spanning two bays. Using Monokote I drew it tight along the leading and trailing edge and along the cap strips of the ribs. I tacked and sealed all the edges and then hit the open bays with the heat gun. It was tight as a drum and seamless. Now months later the repaired area has started to sag and I have tried to further shrink the covering to tighten it up, but to no avail. Has this covering shrunk as much as it's going to? How do I get the covering tight again?