"You did two things wrong"

Yes and the buyer also did the wrong thing.  The eBay user agreement requires "While using the eBay services, you will not: fail to deliver payment for items purchased by you"

The way to handle non payers is:

If you don't receive payment after 4 days open a non paying bidder case in the Resolution center. Then if the buyer doesn't pay within a further 4 days, you can close the case and an unpaid item may be recorded on the buyer's account (you get back your FVF but not your listing fee). Then you may safely relist.  If the buyer has contacted you and you've agreed to extend the payment deadline, you have to wait up to 36 days after the listing ended to close the case.  Don't forget to close the case before 36 days or eBay automatically closes it and you don't receive a final value fee credit.   If the bidder doesn't pay and you close the case they will not be able to leave feedback.  Unfortunately sellers can only leave positive FB, so please don't be tempted to leave a negative comment on a positive FB it is against eBay policy.