I'd take out the binding and trim and then re-bind. You can do that without taking all the binding off--put a pin either side of the flub and just take out the stitches where you need to trim the flub. Start in the center and carefully snip one stitch, then carefully back out the stitches going both directions--if you don't break the stitches you should end up with enough thread to knot where you have the pins--then it's just a matter of trimming and stitching the binding down. I had to do this when someone put the sleeve on the wrong end of the quilt and stitched it into the binding.