Match bobbin thread to back, and pull the front binding over far enough so you cannot see the stitching where the binding is attached. That should keep your bobbi stitches on the back side completely off of the binding. I stitch in the ditch pretty slowly (usually sew very fast) so I can have some control over the outcome. I love love love this technique and have done it many times. Mostly hit or miss the first few times as to where the stitches landed, now slowing down has it spot on!