When I'm embroidering on cotton whether it's for a quilt, wall hanging or clothing, I usually pre wash it to get the shrinkage done before I embroider. I don't want any puckering up after it's washed, especially when my embroidery happens to turn out exceptionally good. I use Magic Sizing instead of starch or best Press. I just like it better and not to sound like a broken record but it's cheap, only 97 cents a can at Walmart. Another thing you can try is using a temporary adhesive spray. I use 505 spray. I often use it to stick my fabric to the stabilizer, especially if I'm floating the project instead of hooping it. Sometimes I'll pin the item to the stabilizer instead of using the spray. There's just so many ways of doing everything in machine embroidery.
Cari