Get a large piece of styrofoam, cardboard or you can put towels on your bed. Wet the panel and pin it square until it dries. Panels are seldom ever square so you have to either compensate (which doesn't work well and is frustrating) or block them the same way you would block knitted or crocheted items. Personally I use my design board because I know it's square and I can use pins on it easily. Depending on what you square it up on you can use your iron or a hair dryer to help it dry quickly.