Block A Little Small

I have on my webshots site my first two blocks I have ever made for my first
quilt. The problem is the Jacob's Ladder Block is not 12 and 1/2 inches, it
is slightly smaller. I but the sashing and corners on the Bow tie block it
looks great. Now to fix the Jacob's Ladder. Would I pin the sashing so that
the seam allowance of the block is short compared to the seam allowance of
the sashing? I hope you understand what I am meaning. Like my sashing would
be a 1/4" seam allowance and my block would have 1/8" seam allowance. Would
that be the right way to fix the problem? My instructor told me we could
fudge it to fix it, but didn't say how. I will call her next time she is in,
but I would like to get it together.

She