AirPlane Sway Effect

Hello everybody
i need little help with this script :

if(horizontal != 0){
	plane.Rotate(horizontal * Vector3.forward * Time.deltaTime * -rotateInt);
	}
		else{
			Debug.Log("get back the rotation to 0");
		}

i use this script to rotate my plane if i pressed A or D,

but i got to problem

1- how to make back to normal rotation if i didn’t press A,D anymore

2-how to make the rotation limited
because if i keep hold A or D, he will keep rotate like 360* degree

thanks

Interpolate the rotation value from your current back to your target. See: Unity - Scripting API: Quaternion.Slerp