I have only pin basted for almost 30 years. You need to get the back down snug but not so tight (like a drum) because when you release the backing, the top will appear puffy. That is because when cotton fabric is stretch, it will retreat back to it's normal shape. Before I put the top and batting down, I run my hands over the backing to make sure it is not too tight or too loose. Do you have a quilt store that you can go and show them your problem?? I have always found shop owners can explain what you might have done wrong. Your LQS should be you best friends especially when you are just starting to quilt.