Then, click on the Account tab on the left navigation panel.
You may see a credit card stored. Delete it by clicking the little trash can.
Please make sure your order didn't process by checking your bank statement, and then go ahead and try the purchase again. (You may also have that card saved to your account. If that's the case, it will be saved in your cards list and you can select that card at checkout. You will have to verify the CVV2 code when using the card at checkout.)