If the second "sale" is not recorded in your eBay purchases, the glitch has corrected itself.
I gather you have been reimbursed for the double payment?
Ask your seller if he shows two purchases. If so, tell him to send you a Mutual Cancellation request. You can either agree or ignore this, and when it closes (faster if you agree), you will be released from the transaction. You then can leave positive feedback thanking him for his courtesy in clearing up the minor problem and he gets his selling fees back.
