I was having the same problem -- mine were HORRIBLE. Then I used these directions: Hair-Hardware.com - Hair Clips, Ribbon, Headbands and more...
and they came out awesome. Here are the ones I've made since then (the blue and white one was the first one I did with these instructions): DCBaby on Etsy - Korkers
I cut the korker pieces to 2.5", but to make sure they were even, I measured the 1st couple and then used those pieces to cut the next few. It turned out that a korker piece cut to 2.5" has 5 "curls" on it, so it was really easy to figure out where the middle was. I used around 35-40 pieces for each korker and got a soft doll needle from Joann's, which is a lot longer and bigger than a regular needle - made it much easier to stack up all the korkers! And once it's all sewn and tied off, just fluff it up a bit to make it more round.
HTH, please let me know if you have any other questions or if I can help out any more. Good luck!