I think sometimes just shifting into zone for a few positions to slow the bleeding helps settle the players down. Sure, they might shoot over top it (or if you aren't used to practicing it, run right into the teeth of it), but it still takes time to break a zone down.
I think it's crazy not to have a zone in your back pocket, especially at GMU's level. We won't have the biggest, longest, strongest, fastest athletes on the floor every game. To ask them to guard man to man exclusively is insane.
As to adjusting: as Gobo said during the Princeton game, "there is no backdoor cut against a zone."