Belgian beers frequently exceed 10% sugar. Duvel, for example, includes 17-18% sugar (don't recall exactly).
To the op, grab a demo copy of brewsmith and fiddle with the number until you reach your desired gravity. I would add a word of caution, the thinner your beer the higher your perception of bitterness will be.
If it was me, I would probably just downscale my water and hops to get the gravity I wanted rather than adding sugar. I would also make sure as heck to use a hop bag when dry hopping this time. I lost way more than I expected last time by neglecting this step.