Where the film landed for you
You kept the film in the middle
You placed your cards - and placed them near the centre.
This is where Kitty Farmer wanted Ling Ling to go, and it is where most of the class would have put her: an X somewhere in the middle, exercise complete. The line lets you do that. It just cannot say what the middle means - which was Donnie’s point, made with a slider instead of a speech.
In the film: The rest of the class: an X in the middle, card handed in, no trip to the principal.