How can I see if a block within a Grid Panel is full?

I’m working on an inventory system. I have some images that I want to span multiple rows/columns while others I only want to be 1x1. My current setup has each going to the locations I’ve specified within my blueprint, but I don’t know how proceed beyond that. I need to somehow check whether a block within the grid panel is already “full” then find the next available location that an item can fit into. Any help would be greatly appreciated. I’ve attached images of what I’m currently doing within my inventory widget blueprint. Thanks!