validity of dates on visa

I go to China for a trip that was supposed to depart on Oct. 28th. The trip has been postponed to Nov. 29th. I was told that my visa was good for only 90 days & that it would expire on Nov. 24th, thus necessitating reapplying for a new one. It states that it is valid until 24AUG2013, and that the duration of each entry is for 90 days.
My visa number is21122750.
My question is am I required to file a new application?
Thank you.