I have the same problem but I'd rather go over the missed sections than do the binding
by hand. I think there are two reasons why we don't reach the stitch line...either we
didn't stitch a straight 3/8" or we didn't trim our quilt properly. It happens.
If you have a lot of miss I would follow coopah's suggestion and cut the binding
a little wider. I've done it and it works better. Most of the time I forget. Oops. LOL
It also helps to do a running stitch along the edges of the quilt before applying
the binding. Do you use washable school glue when applying your binding?
It helps to sew straight because you don't have to struggle with pins, clips, etc.
I glue one side at a time.
I also make a better binding if I remember to make a test piece:-).
For example, a quilt with a piano key border is a lot thicker at the edge and
usually needs more than 2.5". The thickness of fabric and thread will also
make a difference.