Revised dealer return

We have filed our quarerly return for 4th quater of f.y. 2011-12 but subsequently, we found that there was one import purchase which was booked as Excise purchase but the tax invoice was raised instead of central excise Invoice. 

Now, we want to know whether we are required to file revised return by removing the said import consignment? If yes, what is the time limit for filing of revised return?

If we are not required to file the revised return than does it create any legal obligation following the excise rules and acts?

Awaiting your feedback.

Thanks & Regards,

Tushar Parmar.