Every time I use an impression mat the pattern stretches and sometimes to the extent that I have to do it again. Is there any tip I can use to minimize the stretching, especially over large cake sizes?

most possibliy your fontant is too soft.. try using powdered sugar +corn starch for dusting instead of crisco. or try using fondant that is a little stiffer.. ohh and it might help if u dont roll the fondant too thin. thats all that comes to my mind now

I've found that rolling over the mat causes the stretching. I try to press down either with my hand, rolling pin, fondant smoother (whatever works) to get the imprint clear. Hope that helps.

Thanks for the help. I have been using corn starch and icing but may have the fondant too thin!