Thanks all!
FYI, I'm actually tying knots then tying bows on top of the knots. Also I'm using 1/8" ribbon which does not fray as easily as the 1/4" ribbon. I may also tie the loops of the bows together for a more secure bow. Since I'm using 12" lengths of ribbon this should not be a problem as far as looking right on the centers of 3" squares. Had originally thought about tying at the intersection of the squares, but it didn't look right doing it that way.