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.
1) Fold the jacket in half and cut along the length of the back. Using the tailor's chalk, mark 1/2 inch and 1 inch away from the cut length.
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.
In this case, I cut off the strip of fabric off the skirt portion of a dress. One side is hemmed, so I did not need to hem it again.
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.
Difficulty level: 2 out of 5
Machine sewing needed: Yes