Clamp01 does not work?

Hello,

I am making a trigger for a door and I Lerp between start and target positions depending on the ratio value. I want to clamp this ratio between 0 and 1 since the Vector3.Lerp method requires this.

 using UnityEngine;
 using System.Collections;
 
 public class Door : MonoBehaviour {
 
     public bool activated;
     private Vector3 startPos;
     public Vector3 LocalDestination;
     private Vector3 WorldDestination;
     public float speed;
     [Range(0f,1f)]
     public float ratio;
 
     void Start () {
         startPos = transform.position;
         WorldDestination = startPos + LocalDestination;
     }
 
     void Update () {
         if(activated){
             ratio += speed * Time.deltaTime;
         } else {
             ratio -= speed * Time.deltaTime;
         }
         Mathf.Clamp01(ratio);
 
         transform.position = Vector3.Lerp(startPos, WorldDestination, ratio);
     }
 }

The problem is that the varible ratio gets not clamped to 01, it constantly de/increases depending on the bool activated so I have to wait.

Thanks in advance.