How to widen hole through wall header
 

I need to widen a hole I made through 3 2x4's with 2 spade bits. I
made a hole with a 1" bit, then used a 3/4" bit next to it, so that it
overlapped just a bit. Unfortunately I started the second hole at an
angle, and by the time I got down into the last 2x4 the center was
almost into the original 1" hole, and the bit slipped over and
through. Now I have a V shaped hole that tapers too much to be of
use, and I don't know how to widen the hole so that the sides are
parallel.

Anyone have any advice?

Thanks