I LOVE the rope border and that's about the only one I'll use. I'm not that good with shell borders! I know they are supposed to be the easiest to do - but not in my case! lol
Anyway, by looking at your Easter basket cake, it looks like the icing is a little too thin. Also, it needs to be more on top of the cake vs the side of it. I have used 21 before, but mainly for the bottom border and I really like the smaller star tips for the top of the cake, I think the smaller sizes (like 16 or 18 ) look better on the top.
Try alternating colors with it! GORGEOUS!! I made a Dr. Seuss cake one time that has a green/purple rope border - I did 3 green "swipes" and then with 3 purple. Looks SOO good!
Make sure they are the same size tip.