Gretchen from Gertie’s New Blog for Better Sewing shows how she stabilizes a V-neckline with twill tape to keep it from gaping. She used the same method on the armholes so they would keep their shape, too. Go to her tutorial to see how she did it.
Have you read?
Easy Cosmetics Bag Sewing Pattern

The bag is simple, uses very little fabric (about 2/3rds of a fat quarter), has no fussy inside pockets (although you can add your own if you like), and takes me well less than 30 minutes to print the pattern, cut out and sew. But quick and simple doesn’t mean it’s not awesome!
It’s the sort of bag that is versatile enough to be used for lots of applications, not just cosmetics and toiletries. Keep all your pens and pencils in order, use it for a small first aid kit for the car, keep it in your desk at work for a few headache pills and other personal supplies.
Make some for yourself, for gifts or to sell.