So sorry the pattern was wrong. I would not rip out the whole seam. I would snip the threads between the block bottom and the section under it and about an extra inch on each side. I would then cut squares of the blue fabric and sew them on like a snowball block. I wouldn't even remove the blue triangle underneath until I checked the fit. If everthing looked good, I would them cut away all the underlaying fabric back to just the 1/4 inch seam. Then it would be simple to resew sew that section of the seam. I know that doesn't get the perfect fit you were hoping for with the light blue and dark blue but if the blue and tan is fixed to line up, I don't think it will be noticeable. Of course this will only work if you have enough of the blue fabric left. Good luck.