Making UIListLayout use both sides

I am making a phone GUI, and I have a messaging app where I want it to stack on top of eachother when cloned. The issue is, when I insert a UIListLayout, both of the frames stick to either the left side, or the right side, how would I go about them staying where they are on the X axis, but just moving on the Y axis?

Here is how I want it to be:
image