There are times with you do need to cut sizes like that (like doing a square in a square) and it's no different than cutting any other size.
With that pattern, it's important you have the center block the exact measurement. And the three strips that line up would need to be cut so they line up, though you could have the center different than the two outer stripes and that would probably look fine.
The outer setting triangles could all be cut larger (and I would so I could trim them down).