limiting player rotation

So I'm making a simple action racing game where the player drives through a series of tubes but I'm having trouble keeping the player object from getting stuck turning completely sideways. here's an example of the problem.

I'm not good at coding but I've gotten some simple c# scripts running in the game. I've been having trouble finding a good solution as the player will turn completely around over the course of the level and the y rotation will vary depending weather the player is upside down or not. any help is greatly appreciated, thank you.