Here is a little tutorial on how to hem a circle or flounce.
After sewing all the flounce pieces together, run a gathering stitch along the outside edge of the flounce. Pull to gather starting at the beginning of the stitching. Make sure to pull the bobbin thread.
Then fold under the fabric pinning and tucking as you go. Like in the picture.
I use lots of pins.Sew, making sure to avoid hitting the pins.
And there you have it!
I also posted on joanna's journeys.