In short, the higher the OG, the more sugar is in the mix. Because your gravity was lower than the recipe called for only means there isn't enough sugar involved before fermentation begins. This will result in a lower ABV (Alcohol content).
My question is did you brew by way of Extract or All Grain?
Your Final Gravity (FG) is on target with the recipe, however, your OG was off quite a bit so the only way to recover the ABV is to just let it ferment all the way out to 1.000. This will increase your alcohol content another 1%, meaning you will yield about 3% (estimate)
At this moment, your beer will not have much of an alcohol content. You will be looking at about 2% ABV. It sounds like the brew was calling for about 6% ABV and missing your OG (sugar %) is the cause.
Remember that fermenting all the way out means all of your sugars will be gone so the taste will be greatly affected. So you need to make a judgment call....higher ABV or taste? If it is taste you want, then go ahead and bottle now. If you want higher ABV, then let it sit for another few days before bottling. Hope this helps....
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