What do I do when I order something on amazon and they ship but I don't have money?

I recently ordered a shirt on amazon and I thought that after I ordered they had taken money from my card. I spent the majority of my card after ordering and later realized I had never been charged. They've already shipped my order but haven't taken any of my money. What should I do?

option A: receive the item and hope they never hunt you down for cash
option B: contact amazon through the "contact us" link on your amazon account and pay for the item
I'm leaning toward option B but by all means do whatever you think is right...