If you submitted your bid during the Preliminary Bidding period, it's likely that someone submitted a maximum bid equal to yours during the Virtual Sale. In the event that two identical high bids are received, it is Copart's policy to award the sale to the Virtual Sale bidder.
To avoid a tie, Copart's Bid4U system offers an option named Bid Increment. Using the Bid Increment option, you can place your preliminary bid and in the event of a tie, Bid4U will bid one more additional increment over your maximum bid in order to break the tie. If a bidder with a higher maximum bid outbids you, you'll receive an e-mail.