Transparent PNG and stickers (rough edges)

Hi. I created a transparent PNG image because I wanted it to work on all colours of shirt. But on the sticker preview it has weird rough edges. I can’t think how to get it circular and neat. Does the sticker come out with those weird edges or not? If so how can I neaten it up so it’s circular?

http://www.redbubble.com/people/deadman3000/wor...

This is kinda new to me so is a test really. I want products to look good though just on the offchance someone actually makes a purchase. I actually want to make the products to buy for myself ;)

EDIT: Nevermind I decided to put the design in a bubble which solves the problem :)

Thinking, the sharpening applied to the thumbnails, makes the edges appear rough, while there is no sharpening applied to the final image used to make the product.