Create aux track - record two measures of metronome - crop to measures, right click - bounce to clips - 
 
then... when I try to turn it into a groove clip so I can easily stretch it out throughout the song... all of a sudden the 2 measures become 4 measure.....??????  What am I doing wrong - ive done this a bazillion times...?

Sometimes SONAR gets the beat count wrong. Open the clip in the Loop Constructor view and fix the number of beats.