In my HS home ec class eons ago, when we started with a piece of fabric that was off kilter, we stretched it both ways on the opposing corners until it was straight. It should not hurt it to do that unless the printing is all on top of the fabric and might crack (I've encountered some like this - more of a decal than printing). Most panels are printed in such a way that the color penetrates the fabric about half way rather than just sitting on top of the fabric.