This is because you didn't find and open all the treasure chests on that level. Every flying level of the game has from 2 - 5 treasure chests in them, depending on the level of difficulty. You need to find all the treasure chests that have been placed in each level in order to earn all the genie jewels for that level. If you finish a level but haven't collected them all, you can replay the level and try again by tapping the back button in the top left hand corner.