You can take your heating iron and shrink a little of that excess out of the fabric before you stick it. Or go ahead and stick it and let the iron pull the wrinkles out afterward (although that makes the iron a little gummy from the glue). Or you can stick it with a lot of little wrinkles and then iron them out later.

I know this sounds a little sloppy, but shrinkable Dacron is a great fabric to work with. Leave the excess material on until you have it stuck the way you want it. Don't be afraid to experiment.

I am sure others will chime in here, as well. You might also look at this website http://www.s****.com/ for helpful hints on using their product, S**** Lite. It is practically identical to Koverall.