Birthday party dress hem facing

I am sewing the birthday party dress and i am having trouble with the hem facing. I understand how to attach it but even after i fold the edges back my facing is still shorter than the dress by about 2 inches. I have checked all of my seam allowances and made sure i cut out the right size on all the pieces. I managed to attach the front facing correctly. Any ideas what i'm doing wrong? I'm making a size 6 by the way