If there are no bids yet on your listing, you can delete it yourself. You can do this by visiting your listing page and clicking the big red “X” delete button. You will be asked to confirm that you want to delete the listing.
If your auction already has bids, you will not be able to delete it yourself. If you open a support ticket we might be able to delete your auction for you. We cannot promise that we will be able to do it because it depends on the circumstances, but we will try.