Why can I only select one side of a shape in UE4?

I’m new to unreal engine and seem to have a problem. Whenever I place a shape actor from the geometry tab, I can only select one side. I’m following a YouTube tutorial where he scales a cube with x: 500, y: 500 z: 20. He gets a small foundation to build on. When I do that, I get an enormous distorted cube.
Another thing is that when I try placing a material on the cube, the material is zoomed in. It looks way bigger than it should look like.
I’ve tried using a different mode in the modes tab but that doesn’t seem to work. Shift + b also doesn’t help the problem.
To word it better: I want a larger foundation, not an upscaled foundation. Sorry if my English isn’t perfect.

There’re two ways you can place basic geometry. One is:

325653-screenshot-3.jpg

This just gives you a cube. The other is:

325654-screenshot-4.jpg

This gives you a ‘box brush’ which is used for making other shapes.