The main menu should open up as the doors to enter the gym, where you tap "play" and the doors open to start playing.
You are on a gym floor, looking at the other side, where there are 3 kids throwing dodgeballs at you. They should be far away, with a reasonable amount of distance to throw the balls. You have some time to predict when to dodge, but it should still be difficult to play. They all throw the dodgeball in a straight line, where there are three "lanes", and you move from left, back to middle, or right. The kids all throw the balls simultaneously in a random order, where the player has to keep moving. This should be a hard game. This is all first person, and moving left or right, would have the angle the screen diagonally, kind of like where you tilt your head 45 degrees. This should all be smooth transitions when you tap left or right to move from lane to lane. Every ball you dodge, earns you one point, the score should show visibly, but somewhere discreet at the same time..
The game over screen shows up when you get hit. The screen can flash similar to when you blackout, and the score is shown, along with the choice to play again and rate us option.