I can sympathize! Try adding two rulers together and see if that gives you a big enough square. I end up having to do that more often than I'd like. I bought a 12.5" square ruler, thinking it would be big enough for anything I needed since I usually work in small pieces. Well, I now tell everyone who is buying a ruler to get the 20.5" square ruler instead of the smaller one.
I think you're right, no one but another quilter would realize you might be missing a row. Make sure to get a photo of the graduate receiving the quilt. The look of joy on her face will more than make up for all the hassles you've encountered with this quilt. ;)