There are two times you might iron your binding. After you create it you could iron it in half, wrong sides together. Some say they don't do this, but I will always do this because then you don't have to worry so much if the binding is staying together like you want it.
Another time the binding really needs ironing is if you sew it onto the front, fold to the back and stitch in the ditch from the front. That seam on the front needs to be opened very well to expose the seam to stitch into. I used to pin, pin, pin that, but now use the glue and it works like a dream. I never miss any of the binding with the stitching. After the glue is dry and you stitch from the front, washing will relax that seam and the stitching will all but disappear.