If it were me, I would cut the selveges off my fabric and make sure it was 44" wide for a bit more than 44" along the length. Then I would fold it diagonally, taking one corner and folding it up to the opposite edge, in order to get my square. Make sure that the folded double layer (a triangle) is squared up before you cut. Then I would finger press the fold and use that as the cutting line for the triangle. Does that make sense? Try it with a piece of paper first and you'll see how simple it really is. I seldom have 44" in width after prewashing my fabric, so that would be the only problem I see, but you wouldn't really have to prewash for a wallhanging.