I don't know why your wine would be watery or weak. A Sav Blanc does not generally have a lot of body to begin with. Red kit wines tend to be a bit thinner than their commercial counterparts, but that doesn't apply to a white wine.
What was the starting and ending SG? You haven't provided them for us.
What did the kit say should be the approx. final ABV?
If the kits was just made, it will improve in taste over time. Maybe others, who have made a Sav/Blanc (I haven't), can give you more help.