Go to the listing.
At the top , on the left there is a list of links.
One is Contact Seller.
Don't panic.
If the error was in transcribing the credit card number, the payment will not go through. And you will have to start again. Same if there is no money left on that card.
I guess you didn't use Paypal for your payment? When you do, the seller never sees your financial information and in addition to eBay Buyer Protection and the chargeback feature of your card, you would also have Paypal's Buyer Protection.
And the service is free to buyers.