I am a beginner quilter and recently I pieced a small wall hanging. Here is the problem: my squares were good and flat, but when I added the lattice strips, which included some small squares, the quilt became very puffy, and wouldn't lay flat. What did I do wrong, and is there any way to flatten it so it will be easier to quilt? I really tried not to stretch the fabric when I ironed it. Please help, I'm very frustrated with it. Thanks for your time.