That is the reason why I have clothes that can't fit me. Ok, I'll admit that partly is due to an temporal blindness that I am one size, when I am in fact the next size up.
What to do in such cases?
You can either give it away in a swap or to alter it to fit.
2) Measure the shoulder and back width of a jacket that fits. Calculate the amount of fabric needed for the panel. If the width of your normal jacket measures 15 inches, and the jacket you are expanding only measures 12 inches, the difference is 3 inches. You will need to cut 1.5 times the difference plus 1/2 inch on both side for seam allowance. In this case, the amount is (1.5*3 inches+2*0.5 inch seam allowance)= 5.5 inches.
3) Pin the floral strip into place between the two cut halves of the jacket. Baste into place before using the sewing machine. Remember to sew an overlock on the raw edges of the fabric.
4) To further decorate the jacket, cut a piece of the same fabric as the strip and cover the button with it.