[Lucky_star]

Ok here is the solution to your problem.
Open the audio file in the editor.
Click file->Save as.
Select Save as type-> PCM Wave
Goto options. Select Number of Channels as 2(or Stereo).
Give a random name and save it.
Next open this file. You will find your sound in both the channels.

Another way is to play the mono file from a player(Say winamp) and do a stereo recording with Stereo Mix as your your input.