Tax Question!!! My fiance and I were married in Jan 2009 and filed jointly for 2008 in error. What do I do?

I filed our taxes last week on ezTaxReturn.com. My finace and I were just married in the beggining of the year (2009). I filed as married / jointly and did not realize that we should have filed as single and separately, what should we do and what could possibly happen as a result of this mistake?