Take the measurement of your shoulder to under your bust and mark it on your shirt.
Mark two halves on the lower part of the shirt. This will be the ribbon portion of the shrug.
Cut out the ribbon part from the shrug and cut the two halves.
Cut a v-neck that leaves a length that matches your ribbon length, so it will be even when you sew all the parts together.
Open the seam of the two ribbon parts and cut in the middle of your shrug.
Sew each ribbon on each side of the shrug.
Tie it in a pretty bow with the help of your scrap fabric :D