Sometimes I like to pull the backing to the front for a binding. I am having trouble getting the corners to look nice. Is there a secret?

that's why i don't do it that way, i can never get a good corner

The easy way is to overlap at the corners rather than trying to miter. However if you prefer to miter, you can fold under the actual corner so it leaves a diagonal fold that is just right for the mitered corner. May take a few tries to get that fold exactly right, but it works great.