To do this, you need to have a blind hem presser foot for your sewing machine.
Step 1: Folding and Pressing your Hem
Iron it back so the fabric stays how you just folded it.
Fold this under to the desired amount of hem you would like (ours is about 2 inches), so that there is a fold that is created with the fabric right sides together. Iron the fold into place.
Lay it flat again, wrong side up. Take the fold line and line it up so that you only see 1/8 inch of the original hem that you pressed. Press this fold down.