Nita,
relax. While your cabin might not be near midships, it being located on a lower deck rather than a higher deck is good and not bad as far as stability is concerned.
Riviera Deck is also clearly above the water line, so there are at least some 30 foot or so below you before the ship's keel is reached. Your cabin is most definitely not at the bottom of the ship even if it is on the lowest passenger deck.