Message the buyer and kindly ask them to retract your bid or cancel the sale Explain why.
I suggest you don't repeat this in the future because NOT ALL sellers will simply cancel the sale or retract your bid since it's a headache and sellers have to go through a process to get their final value fees refunded by eBay. Also, if the seller opens an unpaid item case against you, and it happens three times, eBay will shut down your account permanently.
