Audio playing out of left side only?

Audition treats files as exactly what they are - asking it to treat them as something else is heading down the road to chaos! There are perfectly workable solutions though:

If you want this as a mono track, then open it in waveform view, go to Edit>Convert Sample Type, and you can change it to being a mono file. If you don't want to do that, and use it in Multitrack view as it is, then you can do this by inserting an instance of the Channel Mixer in the track's effects rack. You can set this so that the left channel also appears on the right channel, and you can use the panpot to position this wherever you want in the stereo field. Either method will work fine