Rotating the weapon back using Quaternion.Lerp

Hello everyone. I want to rotate my gun to left & right when player moves to left & right. So I made a code like this :

  var from : Transform; // a gameObject for start
     var to1 : Transform; // a gameObject which is for left limit of rotating ( 0,0,1.5)
     var to2 : Transform; // a gameObject which is for right limit of rotating ( 0,0,-1.5)
     var orig : Transform; // a gameObject which has the original rotations of gun(0,0,0)
     var current : Transform: // a gameObject for the weapons current rotation
     var speed = 0.1;
     private var rotateLevel : int =0; // a value to stop rotating left
     private var rotateLevel2 : int =0; // a value to stop rotating right
 
 function Update(){
     if(Input.GetKey("a")){
     if(rotateLevel<40){
     rotateLevel+=1;
     rotateLevel2-=1;
      transform.rotation =
           Quaternion.Lerp (from.rotation, to1.rotation, Time.deltaTime * speed);
           }
     }
     else if(Input.GetKey("d")){
     if(rotateLevel2<40){
     rotateLevel-=1;
     rotateLevel2+=1;
      transform.rotation =
           Quaternion.Lerp (from.rotation, to2.rotation, Time.deltaTime * speed);
           }
     }
     
     
     else{
     
   ?????
     }
 
 }

This works well, it moves smoothly & good according to the variables that I adjusted. But when I stop walking, it stays in the position which it was at. So all the aiming and other things get messed up. I need to turn the gun back to it's original rotation smoothly. For that, I made a code like that but didn't work :

 else{
 
  transform.rotation =
       Quaternion.Lerp (current.rotation , orig.rotation, Time.deltaTime *speed);
 }

but as I said it did not work. I need help, any ideas ? Thanks =)