What problem does Katniss face when it's her turn to perform for the Gamemakers?

By this point, the gamemakers have watched 23 displays: they are drunk and disinterested in Katniss. Their indifference to her work, manifested in their attention to a newly-arrived roasted pig, angers her and she fires an arrow directly to their balcony, skewering the apple in the pig's mouth with her arrow. She knows it was a mistake and leaves immediately.