cant regualte the sprint speed of my character,I cant change my sprint speed!!!

So I´ve added an option to sprint to my PlayerMovement. when Im pressing left shift the usual speed is supposed to go to a certain amount. But somehow, eventhough my character gets faster, I cant regulate how fast. I have even gone ahead and made the sprint speed a much smaller amount than the normal speed. Still my character is faster when i sprint mode than if I just walk.

     public float speed = 0f;
     public float Sprintspeed = 13f;
     public float Walkspeed = 10f;
     public float gravity = -10f;
     public float jumpHeight = 5f;
 
     public Transform groundCheck;
     public float groundDistance = 0.4f;
     public LayerMask groundMask;
 
     Vector3 velocity;
     bool isGrounded;
 
     void Update()
     {
         movement();
      
     }
 
     public void movement()
     {
         isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);
 
         if (isGrounded && velocity.y < 0)
         {
             velocity.y = -2f;
         }
 
         float x = Input.GetAxis("Horizontal");
         float z = Input.GetAxis("Vertical");
 
         Vector3 move = transform.right * x + transform.forward * z;
         if (Input.GetKey(KeyCode.LeftShift) && Input.GetKey(Keycode.W))
         {
             speed = Sprintspeed;
         }
         else
         {
             speed = Walkspeed;
         }
 
         controller.Move(move * speed * Time.deltaTime);
 
         if (Input.GetButton("Jump") && isGrounded)
         {
             velocity.y = Mathf.Sqrt(jumpHeight * -2f * gravity);
         }
 
         velocity.y += gravity * Time.deltaTime;
 
         controller.Move(velocity * Time.deltaTime);
     }
 
     
 }

as said before, I have changed the speed to extreme amounts but the sprintspeed is still the same. Would be very thankful if someone explain this to me!