After the recent update the number of beauty points in some of your aquariums might have gone down. That in turn could have influenced your number of beauty stars. Try visiting every aquarium you've already unlocked and check if you collected all three beauty stars. Make sure to check the stars in the aquariums themselves, not in the aquarium selection window.
Please note that the stars bar in the aquarium selection window might appear full when you're still a few beauty points short of getting the last star.
If you're positive that you've collected all the beauty stars, yet you still haven't gotten your reward, please contact our Customer Support, and we'll do our best to help!