I don't know why y value isn't zero

Hello, I’m bringing the ship to the Asset and making a movement.
The ship consists of forward, backward movement, and left and right turns.

After initializing the position and direction of the chip, I pressed the start button and the coordinates of the y-value look like a completely small prime number.

And when you move back and forth or rotate left and right, the numbers get bigger or smaller. Of course, this number is not very large, but a solution is needed because it is likely to affect if it accumulates.

This figure is an initialization code

I don’t use gravity
I don’t know why this is happening.