Its been about 12days and at a temp of about 55F.
That's why your beer's not carbed yet......
The
3 weeks at 70 degrees, that we recommend is the
minimum time it takes for average gravity beers to carbonate and condition. Higher grav beers take longer.
Stouts and porters have taken me between 6 and 8 weeks to carb up..
I have a 1.090 Belgian strong that took three months to carb up.
Temp and gravity are the two factors that contribute to the time it takes to carb beer. But if a beer's not ready yet, or seems low carbed, and you added the right amount of sugar to it, then it's not stalled,
it's just not time yet.
Everything you need to know about carbing and conditioning, can be found here
Of Patience and Bottle Conditioning. With emphasis on the word,
"patience."
You used 8 ounces??? That's almost twice the amount we normally use for a 5 gallon batch. You won't need any more sugar, you need to prep for bottle bombs. You won't need to be worried about under carbed beers at all...maybe just some shrapnel.