Mixcraft displays stereo and mono audio clips in the same way. If it's a stereo sound, the left and right channel are merged into one view.
If you only want to play the left channel of a stereo sound, you can select the sound clip and then click the "Sound" menu followed by clicking "Properties" followed by clicking "Channels" from the menu.
Sound menu > Properties > Channels > Mono or Stereo
> Left Channel
> Right Channel
(Alternatively, you can right click on a clip to bring this up.)
Choose "Stereo/Mono", "Left Channel" or "Right Channel".
The sound clip will display "[Left Channel]" on its title area if it is only playing the left channel and it will display "[Right Channel]" on its title area if it is playing the right channel.