I walk on it. I unroll it with the curved edge digging into the ground. That kind of holds it, as I unroll it. Then, I gently start walking on it, usually in my athletic shoes. After it's flattened, then I cut off the panel I need. If it's still too curly at any point, then I need to walk on it again.
Although it's easier and faster to unroll a long section with the curled edge facing up, this requires a weight or another person holding the edge. And they better not let go or you can get hurt when it springs back on you! After it's rolled out, it still needs to be flipped over, to make the walking on it effective. That's really a two person job.