Can't you just hand sew that part back? Is it frayed?
Here's a cutting chart for different widths of binding.
http://www.quilting-tidbits.com/quilt-binding.html
I followed Amma's tutorial and use Elmers School glue for all my bindings
with my own adaptation. Works like a charm. After sewing the binding to the
top I fold it to the back and pin, pin, pin (making make sure there is enough
to grab it from the front, specially the corners - put a pin through to see
where the needle will hit or not) then go with Elmers glue all around and
iron and remove all the pins. I pin and glue one side at a time so I don't get
poked with pins. Then stitch in the ditch from the front.
The prep may sounds like a lot of work but it's worth it. :-D