You are gonna have to buy a new one..Sorry to say, but since some got really short and no longer fit into the ties, those will never be right and always look bad.
When you do it again, there's a pigtail tutorial somewhere on here (if someone doesn't get to it first I'll look and post it later). It shows how to do it where it'll be zig-zag in the back. It may not be how hers is, but it'll work.. Just do the same thing and it'll look fine.
As for the knots....You bought an epiccosplay wig and it knoted? That's REALLY hard to see lol however if you work really carefully you shouldn't have this problem again. Start out with silicon spray or whatever that detangler stuff is used on wigs (please look it up first), then make the pigtails.
I also found another pigtail tutorial..It makes it so you can't see the wefts:http://www.katiebair.com/wigtutorial_parting.html