I'm so sorry, but there's no way to pledge for "extras" beyond the reward tier you selected.  I would be happy to refund the difference.  Please open a support ticket that includes the email address you used to pledge, what you actually want to get, and the Amazon "Transaction ID".  The transaction ID will be in an email from noreply@amazon.com that says something to the effect of "Your payment has succeeded".  There will be a transaction ID that is a ginormous string of letters and numbers, like HURGABURGA12345SHMOOGEYBOOGEY54321 except less amusing if you read it out loud.  That's the thing to send.