The
issue:
Since
its earliest versions, Finale has had an annoying quirk whereby
you can be left with only one measure in the final system of the
score.
Here's how to fix it: Use the "Mass Edit"
tool (a.k.a. the "Mass Mover" in earlier versions) and
select the last measure of the score. Now press the UP ARROW key.
Voila!
The measure is now included in the previous system. Note that you
can select multiple measures and bounce them down to another system
by pressing (you guessed it) the DOWN ARROW key.