If you used all of the extract in the kit AND you hit your volume, just use the gravity numbers from your kit directions. All of the sugar is there, you literally cannot mess it up.
What happens is that newbs (I did it, too) don't realize that using top off water makes it pretty much impossible to fully mix everything, so your gravity reading can be really high (more sugar in the sample) or low (more plan water in the sample).
The good news is that the fermenation process totally mixes it for you.
- blogging about making my own beer and raising a lot of kids.
Check out the priming sugar calculator
and the beer calorie calculator
Fermenting: Yorkshire square brown ale
Bottled: Belgian golden strong ale, Yorkshire square brown ale, Leffe Blonde clone, imperial nut brown ale