Recently I came accross a card shaped like this. I'm sure the original designer used some sort of die cut to create theirs, because it was perfect. I don't have a die cut, or even a shape like this, so I created my own.
Below you will see the template. To make this I used a piece of 3x6 scrap and folded it in half both directions. I then free handed with a pencil the shape on one of the 4 sections. I then cut that section and the folded an traced it to the other sections, and so on. I hope that makes sense?
This is my card for the Color Me Monday combo over at Jeanette Lyntons blog. Be sure to go check it out, because she has a really cute circle card.