We will need to know your recipe to get a better idea of what happened. If this was a beer where you boiled only portion of the wort and then diluted it with water, it might be something as simple as a batch that didn't get mixed well enough. It would also help to know how much total water you used, and the process of how you went about making the beer.
I used the following in my recipe:
5.5lb amber malt extract
1lb crystal (20c)
Northern hops (boiling)
Cascade hops (finishing)
I did this outdoors on a turkey fryer.
In 1.5gal water, boiled my cracked grains for 30 min, then removed majority of the grains (my strainer's not that good and I didn't have any cheesecloth for steeping). Added the extract, Northern, and gypsum for 60min, and finished last min with Cascade. Sparged into to ~2gal water, topped off to 5gal, allowed to cool to 70 degF, pitched yeast, took the OG, then panicked and came to AHA forums.
When I added the wort to the carboy, I didn't intentionally "mix" it persay, just siphoned in the water to top off the carboy. Maybe it was still in a suspension with the wort when I siphoned off for my OG reading. If this is the reason it was so low, 1) how would I mix it next time, and 2) is there any way to find abv without an accurate OG reading? I'm pretty much without one for this batch. Thanks for the help all.