This is probably coming to you too late for the mitered borders. I saw Alex Anderson demonstrate an easy way to miter borders. I don't know how to describe it except that the borders are sewed all the way along each side stopping and starting 1/4 in from the edge on each side. Then she showed how to fold one side back on itself and press the miter. I tried it and it works well. I wish I could give a better description, but maybe someone hear knows of it and can guide you. I mitered stripes this way and the corners are perfect enough for me.