What is wrong with this instantiate prefab canvas method ?

Hi, I'm trying to instantiate a prefab of a canvas which contain a " boost" bar. Im doing this :

 public GameObject boostBarCanvas; //prefab of the canvas
 public GameObject boostBar; //Prefab of the boost bar image

 private GameObject boostBarC;
 private GameObject boostBarI;

void Start() {

         boostBarC = Instantiate(boostBarCanvas, transform);
         boostBarC.GetComponentInChildren<Canvas>().enabled = true;

         boostBarI = Instantiate(boostBar, transform);
         boostBarI.GetComponent<Image>().enabled = true;
         boostBar.GetComponent<Image>().fillAmount = 0;

}