Small waveform on my final stereo mix track...

Whats your master bus set to ? if you moved your master bus fader, move it back.
Typically I set my master bus to 0dB. this is something you shouldn't really play with, always leave it at odB.
use individual tracks as an accumulative sum  to balance the level on the master bus.
 
Something important to note is your hardware fader (sometimes hidden) all the way to the right in CV view.
Make sure this is set to 0dB as well. once this mix is done it can be feed back in to sonar, then using a brick wall limiter you can boost it, in a process close enough to be called mastering it.
 
You can always use the export function and see if the results are different, however I doubt it.
what you are probably experiencing is the difference between what you hear / vs what you see
and this phenomena comes up all the time.
 
your monitor level, what you hear in your speakers, your hardware level, all play in to what you get during a bounce / mix down / export. its all about trial and error. find a good level using Peak and RMS. trust your eyes when it comes to levels, trust your ears when it comes to balancing. then it should be close.