Question Horizontal Layout Group and Dynamically added items

Hi,

I have made a "slot" prefab that is designed at 64 pixels x 64 pixels.
I've added a horizontal layout group to a game object (container) which scales with the screen size. The horizontal layout group has Child Force Expand selected (width and height).
Then as the scene is loaded I dynamically add 10 of the "slot" prefabs to the container with a MonoBehaviour.

My problem is that the slot remain at 64x64 in size and are not scaling with the container.

What am I doing wrong here?