Fabric Face Collage

I've been working on a fabric collage. I started by painting a piece of muslin with gesso, then I drew the face on it. I colored it with watercolor pencils and then used a wet paintbrush on it. I was happy with the face, but when I sewed all the pieces together today, I had a little problem with the gessoed fabric bunching up. Next time, I might just do it directly on the muslin. But it's my first time painting on fabric, so I'm not too fussed about it.