[Al Skierkiewicz]

Corey,
The voltage difference you note could be explained in a variety of ways. The meter could be introducing the error, the power supply feeding your circuit could be low. (You need at least 2 volts above the output voltage for the regulator to work, in this case V in should be greater than 14 volts. This is called the dropout voltage) or the variation in regulators (production variations.) produces this lower voltage. I am happy to get 11.8 -12.2 volts out of a 7812 especially the garden variety from Radio Shack.
By the way, if the input voltage allows(i.e. it is high enough), you can add diodes(banded end connected to ground) in series witht the ground pin to raise the ouptut voltage in 0.6 volt steps. Two diodes in series with the ground pin would give you 13.2, three diodes would give 13.8 volts.