Image is stretching to canvas.

Here is the code I'm using to try and put a green square on the center of the screen.
What happens is the green fills the entire screen and I can't figure out why. It's probably something very simple that I'm missing, but I'm new to Unity.

I've tried with a regular Image instead of RawImage, and setting the parent to the GameObject or Canvas doesn't make a difference.

Code (CSharp):

1. GameObject mapObject = new GameObject();
2.  
3. Canvas newCan = mapObject.AddComponent<Canvas>();
4.         newCan.renderMode = RenderMode.ScreenSpaceOverlay;
5.         newCan.transform.SetParent(mapObject.transform, false);
6.  
7. RawImage rImg = mapObject.AddComponent<RawImage>();
8.      rImg.color = new Color(0f,1f,0f);
9.      rImg.transform.SetParent(newCan.transform);
10.      rImg.rectTransform.rect.Set((Screen.width/2)-8, (Screen.height/2)-8, 16, 16);
11.  
12. mapObject.SetActive(true);

 

Hi,
You can go through the link given below.That will help you for sure.
http://www.raywenderlich.com/78675/unity-new-gui-part-1

Thanks