sunnycool,
Next time in Sonar, before you convert to mp3, which should be your last step.....you take however many tracks you have laid down, go to the menus and select bounce to tracks, what that will do is merge all your tracks down to a stereo pair.

The bounce to clips option is if you have different things on one track and want to make one solid track out of it, it will join all the clips together.
jam on,
Terry