How to set up canvas and grid pixels to be perfect

Hi community.

I have set up my document 400x 400, but when I put the guides, and turn on the grid, its not perfectly symmetrical to the smaller pixels within the rectangles are of the grid, is there a way to get it all lined up perfectly? and the cavas since its 400 x 400, why is the last large rectangle with half sqaure, and the other half out the canvas?

first image from illustrator 

Second image with guides from PS