Grid

Hey!
Could anyone help me with these guides? (see the brief attached)
I don't think I got it right about the grid system.
I'm confused by the dimensions of the grid modules. They are so small: 2.5cm x 3cm, and 7 columns don't match the margin size, which is W 447mm x H 285mm.
And here are two documents with the grid I've created. (attached)
I would be very grateful if someone could tell me how to set up the grid correctly.
Thank you!