No you don't! If the word 'You've won a house!' was on a piece of paper in a barrell with heaps of other pieces of paper and someone spun that barrell and said, "If you get the piece of paper that says 'house' on it then you've won a house!" and you got that piece of paper, THEN you could say you've won something.
You don't win auctions. Winning requires either luck or intelligence, and forking out cash for something doesn't require either of them.