Very nice quilt. I don't believe you were overpaid. You purchased the materials and it was your time that created it. In addition, it was your machine, the price you paid for it and the upkeep. I don't see my stitching as a hobby the way some people do- it's work. It's work that I enjoy but nevertheless, it's work. Nobody considers my husband's sawmill work a hobby even though he loves it.
Someone mentioned a thank you note and that sounds great. I think it's a wonderful way to keep in contact with your customers. I'm glad to read that you are going to enjoy the money you made on the project. Have fun!