if your intent was to use a miter seam to make a straight strip of binding you can correct it. Cut off or "unsew" the seam you made. To miter for a straight strip, you need to set the fabrics at a 45 degree angle before you sew them then sew them together with an angled seam. I put one piece on the surface, right side up so that it's parallel to the edge of the table. Put the second piece right side down at a 45 degree angle so that the ends of the two are overlapping...make an "L" with the two strips, right sides together). The part where the strips overlap is a square you'll sew diagonally across that to make your miter. If you've laid them out as I've described, you can then stitch from upper left to lower right on that square...but before you stitch, put in a pin and open the two strips to make sure it's the way you want it to go. I mark my stitch line with a pencil since it's on the bias and can be stretched out of shape. Hope that makes sense.