Fold fabric so it is 54" wide by 1 yard.
Fold that in half. where the center is cut you neck hole.
fold all edges in and do a running stich.
Do the same around the neck.
With your machine use a strech stich and follow you running stich.
Try it on, inside out. And mark were you sides meet. Or measure if you want it perfect.
Sew up each side you just marked
when you get to the armpit area turn it in a half circle and sew a parallel line about 1/2 inch ( to the outside)
cut between the two stich lines
Turn inside out and tada all done.
With scraps you can tie a headband.