I personally don't think what fabric you used for the "back" would in any way determine your binding, I also think, unless you are doing a 'quilt as you go' technique, adding a border now that you have quilted the top, might be a bit tricky...adding batting and backing along with border.....so in my mind I works bind it in the dark burgundy and that will act as a frame for your beautiful 'first quilt'. Congrats!