Hm... from my little experience, it's best to carve the neck before attaching the fingerboard. Twice a neck has back-bowed on me after carving. Without a fingerboard attached, you can easily plane or sand the top of the neck level again and then glue on the fingerboard.
In your case I would probably plane the fingerboard level again. I would use a plane rather than a sanding block. Of course, if the board is already radiused, that may not work very well and a radiused sanding block, as suggested by guitar2005, would be better.