Mathf.Clamp not working, and how to keep z to 0?

Hi, I am currently making code on unity C# and I am encountering an error where I cannot clamp xRotation to -90 and 90 degrees, meaning I am allowed to look up and down with no limits, which I do not want. I'm not really an expert programmer and I've been following Brackey's tutorials (The video I was following https://www.youtube.com/watch?v=_QajrabyTJc&t=232s) but this isn't working and I am not sure why.

         //Moving the player and camera dependant on the mouse x and mouse y
         float mouseX = Input.GetAxis("Mouse X") * sensitivity * Time.deltaTime;
         float mouseY = Input.GetAxis("Mouse Y") * sensitivity * Time.deltaTime;
         float xRotation = 0f;
 
 
         //Clamping xRotation
         xRotation -= mouseY;
         xRotation = Mathf.Clamp(xRotation, -9f, 9f);
 
         //Transforming the camera and player on the mouse x
         cam.transform.Rotate(xRotation, mouseX, 0f);
         player.transform.Rotate(0f, mouseX, 0f);
 

That is the area where I am encountering this problem. I would also appreciate if you could tell me how to keep the z rotation to 0, I don't want my camera to be slanted.

Many thanks for any help :)