I can’t see the pictures.
If you mean the text is not centered, just select the text from the editor ( between the shortcode tags ) and select to center it ( the same way you do in Microsoft Word ).
To have 3 grids of 1/3 size, you have to add 3 grids each 33%. You can set the size for mobile and tablet, I recommend 100% for both in some cases, but you can go 50% tablet 100% mobile.
The grids float, so if you set a single 33% grid you will have to use custom CSS on it to make it stay in the middle, otherwise it will align itself to the left.