My object acts wierd, 2 balls being shot instead of one (from different position)

the ball should be shot from one position, not two here is the code:

    public var snowballPrefab : Transform;
public var snowballSpeed : float = 6000;

function Update(){
            if(!snowballPrefab || !snowballSpeed)
                Debug.Log("[Shoot] 'bulletPrefab' or 'bulletSpeed' is undefined");
                var snowballCreate = Instantiate(snowballPrefab, GameObject.Find("SSpawnPoint").transform.position, Quaternion.identity);
                snowballCreate.rigidbody.AddForce(transform.forward * snowballSpeed);

It's acting very wierd. I use a Object as Spawn Point, One prefab as bullet, and everything is set up properly, but there are 2 bullets from two points shot instead of from a point.

Use GetButtonDown instead of GetButton, the latter returns true every frame that the button is held down

EDIT 2: Now it's creating one instance of the object:) Point achieved. Is there any way I can make my "spawn point" unmovable? it seems to move down as I shoot.