You've been getting good instructions here on how to cut the borders and put them on. They get a little stretched or a little scrunched to fit the measurements you made of the middles.
But the binding can be a wave saver, if you can stretch it a bit as you put it on. After the first few stitches have adhered the binding, lay the binding on, give the binding a tug and hold it down with a finger, then put this through the needle. If the binding is WOF, it can be tugged gently; if it is length of fabric, you can pull pretty hard. It doesn't stretch much.