Welcome to cruise-chat.
Sorry to hear the bad news.
You are scheduled to be there from 6pm to midnight, which really means you would be off the ship around 6:30pm and have to be back aboard by 11:30pm. You are missing 5 hours in Canada - at a port where the sole purpose of the stop is to make the cruise comply with U.S. maritime law. That is the only reason they still have to stop, even though nobody can leave the ship.
It happens. Rarely, but it happens. The compensation may seem small, but given the overall insignificance of the port in relation to the whole cruise I can't see NCL offering anything more. It would not surprise me if many passengers weren't planning on leaving the ship anyway.