Wrong assessment year chosen for the efiling of tax return

I had wrongly efiled the income tax return for the assessment year 2012-2013 in the ITR form of assessment year 2011-12. When I enquired about it in the income tax office, they told me there is a demand of tax payable that is shown (for the assessment year 2011-12) because of the wrong efiling. I am worried if a demand notice would come stating that i have to pay tax when i had already paid the tax for the FY 2011-12 (Assessment year 2012-13) and i had no tax to pay for the FY 2010-11 (Assessment year 2011-12). I had contacted various persons for help regarding rectification of this, but i have not received any clear answers. Please suggest what am i supposed to do.