A petticoat will hold everything out further, but if you want the purple layer to stick out right to the points you'll need to interface it. Once it's stiffer it will hold it's own weight up off the end of the petticoat otherwise it will flop past the end.
I can't tell from the photos if you've made the green layer a skirt or puffy shorts. If shorts maybe go for a matching green petticoat over the top of them but under the purple layer. If a skirt save on special fabric and stuff it under the green layer.
Mini petticoats are easy to make (just lots of gathering), but when I needed one they were actually cheaper to buy on ebay than it would have cost me to get the netting, so take a look around if you just need a generic white/green one, unless you already have netting ready
