What does Katniss believe will be the consequences of her action in her private audition with the Gamemakers in The Hunger Games?

Katniss fears retribution from the Gamemakers for shooting the apple.

Katniss volunteers to take her sister’s place as tribute in the Hunger Games because her sister is too young and has no survival skills.  Katniss, on the other hand, is an expert with a bow and arrow.  During the evaluation period where the tributes are supposed to show off their skills, the Gamemakers completely ignore Katniss so she loses her temper and shoots an arrow directly at the Gamemakers.

Without thinking, I pull an arrow from my quiver and send it straight at the Gamemakers’ table. I hear shouts of alarm as people stumble back. The arrow skewers the apple in the pig’s mouth and pins it to the wall behind it. Everyone stares at me in disbelief. (Ch. 7)

The arrow does not actually hit anyone, of course.  Katniss is not ready to murder.  She is demonstrating her contempt for the games and all they stand for with this gesture.  She has had it, and her emotions got the best of her.

Katniss is convinced that her actions will get her into big trouble. The Capital is not known for its sense of humor, and does not appreciate acts of defiance or rebellion.

Now I’ve done it! Now I’ve ruined everything! If I’d stood even a ghost of a chance, it vanished when I sent that arrow flying at the Gamemakers. What will they do to me now? Arrest me? Execute me? (Ch. 8)

She knows that she is at the mercy of the Gamemakers, and has been since she volunteered.  Actually, she has been at their mercy for years because she had to buy extra entries into the games just to feed her family.  She knows that they can do anything they want to her.  She is afraid they might take retribution by targeting her family.

Katniss cries until dinner, and then when Haymitch asks her what happened she tells him.  He tells her that they will not arrest her because it would be a pain to replace her, and they will not likely take retribution against her family because people would ask questions.  What had happened was private, and no one but the Gamemakers knows about it.

Portia tells Katniss that scores only matter if they are very good.  When she receives a very high score, an eleven, she is shocked.  This score makes her a target for everyone in the games.  They know that she is good.  The Gamemakers got their revenge.