First batch and extract batch or all grain? If it was extract, it's hard to mess up the OG. Either didn't add all the extract, added too much top off water, or didn't mix the top off water fully and you're just reading more top off water than wort (the last is the most frequent). In the last case fermentation will mix it all up for you. Regardless, nothing to do now but let it ride.
Outside of determining yeast pitching rates (which I base on my estimation from my recipe) OG isn't really a critical number anyway (unless you're trying to fine tune your process or need an approximation of your beer's ABV)
Provided everything was properly sanitized, you'll be fine.