Call your administrator and have them fix it. It won't be a problem if they fix it before it is reported to the IRS. Worst case you can do a mistaken contribution withdrawal and then redeposit it as a 2013 contribution. It may automatically be applied to 2013 since it exceeds 2012 but it would be best to have the administrator fix it.
If something cannot endure laughter.... it cannot endure.
Patience is the art of concealing your impatience.