CanvasPanelSlot SetSize not working?

I noticed that If I am creating a widget and adding it to a canvas in c++ that I am also unable to SetSize on it, it is forever stuck with a minimum of 100x30. Is there any way around this?

code:
image

Canvas that is being added to:

What I am adding to the Canvas:

result (the space to the right is the extra space from the 100x30 default:
image