Graff only has a VERY light carbonation at 2 weeks

I tried to prime my gallon batch of half Heffeweizen/half graff with about 1/3 cup of apple juice concentrate. It didn't seem to carb much at all and they are at the 2-3 week mark in the bottle. I left it in the fermenter for about 3 weeks before bottling. I was wondering if I could pour it into a bottling bucket and add more priming sugar, then re-bottle to get some carbonation or am I SOL at this point and its going to be a still cider/heffe? Taste is really good it just really needs some carbonation.

Thanks!