I was making some oven gloves the other day and was having a terrible time with the back puckering! I ended up unpicking everything I'd done, because they were horrendous! The wadding I was using was thicker and seemed denser than normal wadding, and my mum suggested that perhaps my presser foot was putting it under too much pressure, which was kind of gathering up the back. I reduced the pressure and it looked waaaaay better! Now I just have to remember to put it back to normal once I've redone them all!