lower than expected SG

so i brewed up an ipa last night, my only issue was that my SG was lower than i expected... i got 1.042 and i was expecting more like a 1.050 or higher. i did have some boil-over, maybe 12 ounces total wort lost, maybe that has something to do with it... with it being in the fermenter now, i would assume its too late to compensate for it. but if i happen to run into a similar situation in the future, is it possible to adjust the SG once the wort is boiled? adding some sugar water maybe? thanks

sugar ferments completely.
Malt extract does not.

so, sugar will raise your Original Gravity, but can result in a lower Final Gravity.

Now that said...let me guess..you boil 2 gallons, then top off with 3 gallons of water in the primary?

If so you DID hit your OG. its very very hard to mix 2 gallons of wort into 3 gallons of water evenly. You get a non uniform solution, so your gravity reading is off.

You basically cannot miss OG in an extract recipe unless you don't add enough extract, add too much...or add too much/not enough water.

Extract has no efficiency like partial mash or all grain brewing...because the extract always gives you the same gravity. mashing does not.

good point, thanks, i didnt think of a non-uniform soultion. i do a partial extract 3 gallon boil and add 2, which would def lead to a non uniform solution. i did lose a small amount of wort and added a little water to get to my 5 gallons, and a non uniform solution, this must be the reason. as far as remedies for this issue, is there a formula or something, maybe an interesting project...

The guys at the local brew shop said from the start to boil as close to the final recipe as possible. So a 5 gal boil is where it's at from what I understand.