Cubase 5 mastering

I am trying to master in Cubase studio 5.0 and my panned guitars and vocals are not mixing down fully. It only has one guitar and one vocal instead mixed down, then it tells me to add multiple tracks to the mix down which will add a whole duplicate song to that one distorting and messing up the master. How do I resolve this?? Also when just one mixdown track is in there the guitars are no longer panned. they are flat!