What ist the best way to create a precise gyroscope motion controller for a "Ball Rolling Mobile Game"?

Hello everyone

I am creating a mobile game in witch you roll a ball through a world and it should be controlled whit the phones gyro. I found the following to be kind of working:

Is that a good way to do it? Do you know about improvements?

Is there a trick to set the default phone position new, so one could calibrate the holding position of the phone in the pause menu?

I am struggeling since 2 days and decided to clean up, what works and ask you.
Thanks for your help!