These relate to blocks not quilts, but these Sharon Schamber videos present some options.
I can't find the video where she was squaring a quilt - not trimming it, but squaring the quilt center, then the inner borders, and then the outer ones, making sure there were perfect 90 degree corners at each step.. I'm thinking it might be within one of her other videos.....sorry.
But the concept is the same. Watch these videos about manipulating blocks into submission (without trimming)
and you might find these methods work for your situation.
It would be a shame to whack off any of your lovely masterpiece.
(Some have 2 parts.)
Shrinking block part 1 of 2
http://www.youtube.com/watch?v=i6aplw_tVZc
How to true a block part 1 or 2
http://www.youtube.com/watch?v=v-3RIWhBvcA
Stretching a block
http://www.youtube.com/watch?v=sQkF02vpVuw