Bummer! The best tip for cutting borders is one I got from Quiltville:
"Lay out the quilt on the floor, smoothing as you go so it is straight and flat, but do not stretch...just let it lay flat. Now take your border strip and lay it down the CENTER of the quilt, top to bottom, just smoothing it out. DO NOT STRETCH, just smooth, smooth. Trim it off at the bottom of the end of the quilt. I lay my quilt out on carpet, so I also like to anchor the beginning end of the borders with a couple of long pins stuck into the carpet. It keeps that one border end from creeping as I smooth. Cut the second strip the same way."
"This has ALWAYS worked for me, because when you are dealing with measuring tapes, they dont drape and lay the way your fabric does....your border fabric is your 'measuring tape' and as you smooth it across the center of the quilt top it will lay the same way as the quilt center with no tension on it."
http://quiltville.blogspot.com/2005/...der-hints.html
I often put a board on my bed and do this because it's longer than the table and I don't have a lot of floor space. When I do, I start with a straight edge even with one edge of the quilt and pin every foot or so without stretching the fabric. When I get to the end, I take my mini mat, rotary cutter and ruler and trim it even. I fold and pin or press each border piece and the quilt in 1/4's and match up the pin/folds on the borders with the center of the quilt. I use lots of pins and ease in any fullness. Works great, my borders are always the right size and never wavy.