At 1.000, it was not done. When you added more sugar, you also are increasing the alcohol. You will have rocket fuel if you're not careful. At 1.100, you would be about 13% alcohol and then then another 3 cups of sugar will boost that even more as well as continue fermentation.
At this point, it would be best to put it into 2 one gallon carboys to decrease the head space, or a one 3 gallon carboy with sanitized marbles to decrease the headspace. You have way too much headspace and are headed for oxidized rocket fuel.
So, I'd siphon it into new (different) sanitized gallon containers and let it sit under airlock for about a month, or until the sg is under .996. Then rack every 45 days or so as long as you have lees (sediment) in the bottom. Don't add more sugar until you have stabilized and the fermentation is completely over.
I suggest reading alot to keep you occupied while you're waiting! This is an awesome place to start: http://winemaking.jackkeller.net/basics.asp
And, feel free anytime to post questions, especially about stabilization and finishing fermentation. We'll try to help!