Help! Player won't stop moving when I release the W key,Help! Player won't stop walking when I release the W key

So when I release the W key for a short second, it stops walking. But after a couple times it just continues walking and won't stop. I'm following a Youtube tutorial and I don't know where I'm going wrong.

Link to video: https://www.youtube.com/watch?v=ReauId6jFFI

My code:

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class KnightController2 : MonoBehaviour {

 float speed = 4.0f;
 float rotSpeed = 80.0f;
 float rot = 0f;
 float gravity = 8.0f;

 Vector3 moveDir = Vector3.zero;

 CharacterController controller;
 Animator anim;

 // Start is called before the first frame update
 void Start()
 {

     controller = GetComponent<CharacterController>();
     anim = GetComponent<Animator>();

 }

 // Update is called once per frame
 void Update()
 {

     if (controller.isGrounded)
     {
         if (Input.GetKey(KeyCode.W))
         {
             anim.SetInteger("condition", 1);
             moveDir = new Vector3(0, 0, 1);
             moveDir = moveDir * speed;
             moveDir = transform.TransformDirection(moveDir); 

         }
         if(Input.GetKeyUp (KeyCode.W))
         {
             anim.SetInteger("condition", 0);
             moveDir = new Vector3 (0, 0, 0);

         }
     }
     rot += Input.GetAxis("Horizontal") * rotSpeed * Time.deltaTime;
     transform.eulerAngles = new Vector3(0, rot, 0);

     moveDir.y = gravity * Time.deltaTime;
     controller.Move(moveDir * Time.deltaTime);
 }

} ,So when I release the W key for a short time the player will stop walking, but after a few times it continues walking and won't stop. Not sure what I'm doing wrong. I followed a Youtube tutorial and code seems to match..

Video I'm following: https://www.youtube.com/watch?v=ReauId6jFFI

public class KnightController2 : MonoBehaviour {

 float speed = 4.0f;
 float rotSpeed = 80.0f;
 float rot = 0f;
 float gravity = 8.0f;

 Vector3 moveDir = Vector3.zero;

 CharacterController controller;
 Animator anim;

 // Start is called before the first frame update
 void Start()
 {

     controller = GetComponent<CharacterController>();
     anim = GetComponent<Animator>();

 }

 // Update is called once per frame
 void Update()
 {

     if (controller.isGrounded)
     {
         if (Input.GetKey(KeyCode.W))
         {
             anim.SetInteger("condition", 1);
             moveDir = new Vector3(0, 0, 1);
             moveDir = moveDir * speed;
             moveDir = transform.TransformDirection(moveDir); 

         }
         if(Input.GetKeyUp (KeyCode.W))
         {
             anim.SetInteger("condition", 0);
             moveDir = new Vector3 (0, 0, 0);

         }
     }
     rot += Input.GetAxis("Horizontal") * rotSpeed * Time.deltaTime;
     transform.eulerAngles = new Vector3(0, rot, 0);

     moveDir.y = gravity * Time.deltaTime;
     controller.Move(moveDir * Time.deltaTime);
 }

}