Can't resize image properly in script? Need help

Im new to Unity and need help with resizing images.
Ive searched for long on internet but I can’t find an answer for this:

I created a FPS where the Player has an Ultimate Charge. Ultimate Charge charges from 0% - 100% depending on how much damage the player deals to enemies. If Ultimate Charge reaches 100% you can use an “ultimate ability” and the Ultimate Charge turns back to 0%.

I have a UI image displaying my Ultimate Charge. I want this image to become bigger when the Ultimate Charge reaches 100% and get smaller again when it is 0% (when i use the ultimate ability). So, I tried this with sizeDelta and it only works oneway: the image becomes bigger at UltimateCharge = 100% but afterwards it does not become smaller again when it is 0-99%. help please!

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class UltimateImage : MonoBehaviour
{

//scripts
public PlayerShoot pS;

//sprites
public Sprite ultimateNotCharged;
public Sprite ultimateCharged;


void Start()
{
    
}


void Update()
{
    changeImage();
}

void changeImage()
{
    float ultimateCharge= pS.ultimateCharge;
    var ultImageTransform = transform as RectTransform;
    if (ultimateCharge >= 100f)
    {
        ultImageTransform.sizeDelta = new Vector2(140, 157);
        GetComponent<Image>().sprite = ultimateCharged;
    }
    if (ultimateCharge<100)
    {
        ultImageTransform.sizeDelta = new Vector2(105, 118);
        GetComponent<Image>().sprite = ultimateNotCharged;
    }
}

}

Restarting Unity seemed to have solved the issue for me.