I don't have a before picture, but get the shirt you want and cut out a long strip of fabric.

Fold over the edges and hot glue it to itself to neaten it up and prevent fraying

do this on both sides

When doing this try to make the ends the same length, you can see in the next picture that one side is bigger than the other.

put it around your head to measure, hold where you think is a good length. (it's better to be too big than too little, you can always bobby pin it back)

What I did was hold the two ends in place then turn it inside out so I could glue.

Flip in right side out and there you go =)