I've had that happen. Bought some fabric that had panels that I wanted to use. Cut the "square" out and found out it was a rhombus. So I went to a different store and bought some more...and it was not square either. I did this four times...I'm a slow learner...before someone finally told me that when the mfg does a run and if they don't get it square, all the fabric in that run will be off square. So I bought some fabric from the same design line and added borders to square the panel up. Once the quilt was finished you could not tell that the original square was a rhombus.