Next you need to pin the rest of the shirt up the front, where it should button up. Try to keep it as straight and as neat as possible.
Then you need to measure the length of your elastic, mine was 2 cm. Measure about 5 cm down from the top of your shirt and mark it with a pen or a piece of chalk all the way around. You also need to cut the across the top with pinking shears to stop it from fraying. If you don't have any of these scissors, just stitch a straight line across the top, about 5 mm to the edge.
This is how I styled it, using the matching collar as an accessory :) Happy DIYing!