I think if you run a warm iron over the placemat it will fuse the the interfacing back togather so you won't get an air bubble. That is what I did when I embroidered placemats, the instructions said to do this if it separates.
Ok, thank you I will give that a try. Also my sister said that since I have one that is messed up to try and take the corner apart and see what they did. there is one piece of interfacing that is ironed on to the back they did not attach it to the other layer. I will try ironing it. I also had some sewers double stick tape that you can sew through and then it washes away. I hope I can get these to work out, because the napkins came out really cute and other then the wrinkles in the one I did no the placemat looks nice too. Used "Easter Candy" from EmbroideryLibrary.com . It is a chocolate bunny with candy and eggs.