The ship currently wraps in the x axis and limits in the y axis. Some other options include:
Make the x also limit so players can't dodge in this direction.
Make all of the walls kill the ship. This would increase difficulty and we should also color the walls a menacing color to remind the player of danger.
I would agree with limiting the x position so that you can't warp around to the other side. I think it would be useful if players could pin themselves against the wall in this way and shoot straight up the side.
I don't agree with making the walls kill the ship. It seems like adding unnecessary and annoying difficulty. I feel like the only way to die should be from not shooting the balls down fast enough instead of just hitting the walls.
The ship currently wraps in the x axis and limits in the y axis. Some other options include: