Thanks Red. I don't think a tug will do it in my case! Some of them are really off kilter and I think would look bad in a quilt. I'm thinking of a series of rectangles, like a brick wall almost. So it's looking like I'll have to cut the pieces on the lines to make the plaid straight.
Or perhaps I'll set the off kilter ones aside for a different project entirely!! Something smaller so the waste that I have to cut off won't matter so much.