Been there done that. Sooo many times. I don't think you need to take the whole thing apart. Just take that white saddle square out, with a few stitches into the brown colored seam. You should still have enough of the seam on the brown floral to ease in the saddle square. Use a small ruler and marking pen or chalk to straighten up the square. Pin and baste stitch the sides down first. Press. Measure again. If the sides of the brown floral are balanced, pin and baste stitch the top of the square to the brown. Press. Measure again. If the sides are eye appealing, sew with your normal stitching on machine. This is how I do it. Merely a suggestion. Others may have another idea. I truly believe this will work for you.