In extract brewing, all of the conversion, or most of the conversion, of starch to sugar has been done for you. ie: It comes with the malt extract, which is a known amount of sugar. When mixed with a known amount of water it will come to an OG, as long as it is mixed properly...and it can be really difficult to mix it up well. Steeping grains can add a few points, but certainly not 12 points.
so you probably were much closer to 1.056 if the kit predicted the gravity right. there's really no room for error other than not getting all of it in the pot, not measuring water correctly, not stirring the snot out of it.
If you post the recipes somebody will tell you the predcited OG, but i seldom see them wrong.