Mouse locked in center

I have a script that allows me to pick up objects when my mouse is over the object. The only problem is, the mouse is constantly drifting to a side. I created a simple cursor lock script, but it only made the cursor invisible. Which script reference would make it so the cursor locked in place, almost like a crosshair? I got rid of the script that made the cursor invisible, but I have the pick up script here

`private var pickObj: Transform = null; private var hit: RaycastHit; private var dist: float; private var newPos: Vector3;

function Update(){

 if (Input.GetMouseButton(0)){ // if left button creates a ray from the mouse
     var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
     if (!pickObj){ // if nothing picked yet...
         if (Physics.Raycast(ray, hit) && hit.transform.tag == "Pick"){
             // if it's a rigidbody, zero its physics velocity
             if (hit.rigidbody) hit.rigidbody.velocity = Vector3.zero;
             pickObj = hit.transform; // now there's an object picked
             // remember its distance from the camera
             dist = Vector3.Distance(pickObj.position, Camera.main.transform.position);
         }
     }
     else { // if object already picked...
         newPos = ray.GetPoint(dist); // transport the object
         pickObj.position = newPos;   // to the mouse position 
     }    
 }
 else { // when button released free pickObj
     pickObj = null;
 }

}