2" seems like an awful lot for it to stretch. I also agree with Tartan. You may want to try dousing the piece in water and letting it dry flat and perhaps block it to see if that helps. Also keep in mind that the quilting process, especially if you plan some dense quilting, will further distort it. I think if this were mine, I would draw a chalk line where it would be square. Because you say it is a background piece I am assuming (perhaps wrongly) that your plans are to do some sort of applique on it. So I would applique as though the chalk line were my edge. I would complete the entire piece but before binding I would measure again and then cut to square if it is still off that much. Then I would block the piece.