To sew this wing on you need to fold back the backing fabric and baste along the edge to set the seams so they won't come undone when you are turning the wing right side out.
Then let the backing fabric go back into place and start at the end of the basting that you just did. Make sure you backstitch.
then continue sewing around the wing following the edge. If you like you can clip the fabric in the hollows but I didn't. It can make it easier to turn the hills inside out. Make sure you remember to backstitch when you end. Leave an opening to turn the wing right side out.