Adding more sugar

[Moonrise]

Hello - I'm new to posting but not new to reading.
On a whim I decided to make two one gallon batches of juice based wine. One being apple and one mixed berry. Both are natural, no additives.
Ive done this before and all is fine, They are happily chugging in carboys
(having a fruitfly issue and so skipped the primary but will sterlize a rod and stir daily for the first few days)
I realized I only added a cup of sugar instead of a pound.
Should I just reheat some juice, add sugar, let it cool to room temp and add to the carboys? Or leave as is?

 

[bernardsmith]

what was the starting specific gravity? If it was lower than the gravity you are looking for (the potential level of alcohol by volume) then I would simply add additional sugar to the wine and if you pitched the yeast a day or two ago I would simply agitate or shake the liquid to dissolve the wine rather than heat fruit juice. Heating juice encourages the pectins in fruit to set and that is fine if your preference is for a cloudy wine or jam. Worst case, you might dissolve the sugar in a very small amount if warm water but the sugar will dissolve in the fruit juice and the yeast will get at that sugar.

 

[Moonrise]

I didn't check the starting gravity- silly I suppose but normally I just play it by ear with the small batches. I didnt have a container deep enough for the hydrometer and with my fruit fly invasion (harvest time with our Quince out back) I just wanted to get it neatly and safely airlocked.
I have left over juice from what I used Could I bring that to room temperature, add sugar and shake and just add that? I left headspace for fermentation so could add a bit more just to get the sugar in.