instantiate not working properly (javascript)

Hi. I am working through some tutorials and getting to grips with scripting. I have created a simple script to instantiate an object to fire at a wall of blocks i have built. the problem is that as soon as i press play to test the game it is already instantiating the object before i press the mouse button(fire1). Could someone please look at the script and tell me if there is something wrong with it. Thank you.

var bullet : Rigidbody; var power : float = 1500; var moveSpeed : float = 5;

function Update (){

 var h : float = Input.GetAxis("Horizontal") * Time.deltaTime *
  moveSpeed;
 
 var v : float = Input.GetAxis("Vertical") * Time.deltaTime *
  moveSpeed;

    transform.Translate(h, v, 0);

if(Input.GetButtonUp("Fire1"));

      var instance: Rigidbody = Instantiate(bullet, transform.position,transform.rotation);
      
      var fwd: Vector3 = transform.TransformDirection(Vector3.forward);
          
          instance.AddForce(fwd * power);

}