What were your volumes achieved? Often brewers (my old self included) think they missed conversion efficiencies when they in fact added too much water during the process somewhere.
Checking SG Pre boil ( and throughout sparging run-off) helps determine conversion went well and that you hit the right volumes with your water additions also. I Monitor the SG while boiling, make a quick cooled sample for SG readings. When topping up the kettle, I check SG first so as to not add too much water. Let the SG be your guide, not just the volume markings.
If you made too much beer and the gravity is low, I have found that boiling an additional 30 minutes with lid off helps.
As a last resort you could add DME, but I have never done that.
If you monitor and adjust for low gravity all along the process, you shouldn't have to bump it up. If your conversion is a bit low you will just make less beer at the right gravity. I like to make my batch sizes a little larger to account for losses as well, which helps achieve gravities better if you closely watch the water additions. CHEERS! and thanks to Beersmith and its forum, I love it
