Oh, this is beautiful so far! Your colors are gorgeous. If it were mine, I'd add enough rows to make the drop just long enough to cover the sides of the mattress (15 inches, roughly) on 3 sides, and enough rows to reach the top edge of the mattress. Then I'd bind in the darkest plum. I would not add a border ; I think that would detract from the design. And Maybe make two pillowcases--dark main, lighter flange, medium trim (if you do the "magic pillowcase" as seen on youtube).