Tip for Squaring Up

Yesterday I made the unpleasant discovery that the square background for my Hoffman circle wasn't perfectly square in spite of all my supposedly careful marking and cutting. Since the circle has to look exactly centered, I couldn't just trim. I was hopelessly confused about what part to cut, but solved the problem by making a square of paper the correct size (34 inches), and then putting that over the inaccurate piece. I could see the outline of the circle through the paper, so it was relatively easy to move the paper until the circle was centered, and then cut along the edge of the paper square. I don't think I had this idea by myself. It's one of those things that I read somewhere and had buried in the unconscious until needed. I thought I'd pass it on. The top of the Hoffman is finished now; I'm sending my sewing machine to rehab before I quilt it. We need time apart, for sure!