[Unity-Spine] Why is the Spine SkeletonAnimation instantiated so small?

Hi everyone, I’m a beginner of Unity 2D scripting, and I just learned something about 'Intantiate'. So just for fun, I was trying to instantiate a prefabed spine animation in a scene, while I met some problems with it. Is there anything that I did wrong?

My situation:
1. I have a prefabed spine skeleton animation;
2. I have a canvas in the scene containing a UI button to instantiate a new prefab of this animation when pressed.

My problems:
1. After instantiating the animation, it was too small to see. I had to resize it to 100 times to see it. And I was pretty sure it’s not instantiated as the child of the UI Canvas, so its transform wasn’t the RectTransform;
2. I could only see it in the Scene window while I saw nothing in the Game window.

My code is here:

Code (CSharp):

1. public class CreatureGenerator : MonoBehaviour
2. {
3.     Vector3 generatePos;
4.  
5.     [SerializeField] GameObject creaturePrefab;
6.  
7.     void Start()
8.     {
9.         generatePos = new Vector3(Screen.width / 2f, Screen.height / 2f, 0f);
10.     }
11.  
12.     public void GenerateCreature()
13.     {
14.         GameObject creature = Instantiate(creaturePrefab, generatePos, transform.rotation);
15.     }
16. }

Thanks so much in advance.