You have a problem using too much sparge water/not boiling off enough. You may also have an efficiency problem (poor crush, perhaps). Fix the boil-off issue by using 1/2 gallon less water.
Have you calculated your efficiencies? Put everything in a recipe calculator and adjust the volume to what you got, then adjust efficiency until you hit the actual, measured SG. Do this for all your brews, then see if your efficiency is consistent. In the future you can adjust that before you make a recipe, so that you'll hit your numbers.
Also, don't feel bad. Unless you spill extract everywhere, it's impossible to miss your numbers with that method. With AG, there are variables, and it takes time to get things consistent. It took a few batches of milling my own grain to get the gap set and my system down, but after a few, I hit 85% pretty consistently (unless using wheat). For the wheat, I'm going to try milling it a bit finer to see if I can hit that same eff for all my batches. Press on!