If you have one handy, a knitting machine makes fast work of this long strip. We used up a bunch of yarn we had that's too thin for pretty much anything but gauzy ruffled scarves.
Fold the long strip in half, right sides together, and pin. Use an iron if your fabric is very curly.
It was helpful to us while ironing to roll the pinned part of the (very long) strip around a cardboard tube.
Use a zigzag stitch to capture these threads as you sew the seam on the scarf-- these threads are now a drawstring on which you can bunch up the fabric to create ruffles.
Turn the entire scarf right side out by sticking your arm through the knit tube, gathering up the tube on your arm, then grasping the end while pulling the tube back off of your arm.