Me, too. Not so much by the final results but by the 10 point miss. I usually get around 82% conversion with decoction mashes, applying the math to your results would indicate you started with around 11 pounds of grain (Just over 11 pounds, 2 ounces). Wasn't this an Oktoberfest? If that's the case, your gravity isn't really too low for the style. But if you wanted to bring it back up to 1.057, add about one and a half pounds of DME to the end of the boil. You missed target by about 60 GP (10 points times 6 gallons of wort). A pound of wort yields 42 ppg. Dividing the 60 you need by the 42 a pound of DME yields gives 1.43 pounds of DME.
I've seen the recipe but can't remember how many pounds of grain you started with. I'd start looking there - maybe there wasn't enough either due to a recipe miscalculation or a measurement error. Next stop would be the temperature in the mash tun during the decoctions. If it got too cool, maybe the enzymes slowed or stopped working. After that, you're getting into uncommon problems like old grain or high mash pH.
I'm guessing it's after the brew day, ferment it and see what you get! It will likely be a very quaffable Oktoberfest.