Steeping grains wouldn't add 8 points of gravity, and it's virtually impossible to miss your OG on an extract batch unless you get the wrong volume in the fermenter and/or leave out some extract.
More likely is that the wort wasn't thoroughly mixed after you added your top-up water, and you got some of the more watery part...a common, oft-posted problem around here.
Your beer will be fine; the yeast will (or have, given your fermentation activity) find the sugar.
