This feature to mark as unpaid is not available anymore or not as of right now. I just made this mistake myself. I called customer service and they said it would not let me print a label until it was paid so that was very good to know. It is my first time selling on ebay and I can't believe I clicked that by accident in the drop down. They said it would be ok and very helpful. I think that because I was excited that I sold something I was quite worried about messing it up.