This problem I had quite a few years ago, was not a panel, but a long piece of fabric. It was a 9 yard piece. It had been folded like a sheet (not selvage to selvage) for a long time. It was given to me from my neighbor whose wife, and my quilting friend, had passed away. I could not fold it correctly with the selvages together. It was all wonky. I had almost given up on it but did not want to waste all of that quality fabric. My solution was to start on one end and spray mist that section and smooth the fabric out with both hands. I did that for the whole length of fabric, one section at a time. I felt like it was a miracle! it relaxed the fibers back to normal and the fabric laid out smoothly. I hope this will help someone else with a similar problem.