I think I'd add either another row of the gray background stars to each end or a strip of one of the colors to each end to add length. You could also sew strips of the four focal colors together then cut on the diagonal to make a ///// strip on one end and a \\\\\ strip on the other before adding your borders. After cutting your strips and then cutting the length to whatever you want, 3,4, or 5" just move down the width of your strip each time you sew one on then all you have to cut off will be the jagged triangular edge.