Inventory UI Not Filling Screen.

Hello! I was following a tutorial series on how to make an inventory. Everything is ok but i cant figure out how to make the inventory window fill the screen. I’ve set the size box width and height to 1920x1080 but still doesn’t work. I’m a begginer at this so any help is appreciated!
Tutorial: Unreal Engine 4 Tutorial - Inventory System - Part 2 - The User Interface - YouTube
The Problem: Imgur: The magic of the Internet
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