Feel free to wait for other answers from people who like Ionic’s grid component, but I’m not one of them.
First question: do you really need a grid, or can your layout realistically be described in a single dimension, like the text in this paragraph? I’m writing it linearly, you’re reading it linearly, but visually it’s presented with line wrapping that makes it seem like it’s two-dimensional when it really isn’t.
If the answer to that is “all I really need is one dimension”, I’d suggest reading this flexbox guide, which covers centering on either axis, among many other layout properties.
If the answer was “really need two dimensions”, then go for this grid guide. Steeper learning curve, more complex, more powerful. Again, centering is covered in detail.