Remove all of the pins from the ruffled edge, fit the other side of the cushion onto the side with the ruffle sewn onto it, and get to pinning, once again. Match it and pin the entire thing with the pins being approximately 1″-1 1/2″ apart.
The pinning takes a good while, however, it will save you tremendous headaches as it keeps the fabric in place. Otherwise, you will find that your stitch has sewn a few crimped edges. Not good!!! As you see in this photo, My hand is inside the portion that I was to leave open. This will be where you turn the cushion inside out and begin the stuffing process.