Maybellene,
I made a similar fan shroud for my street rod from an aluminum cookie sheet that was the exact correct size. Air flow got blocked in corners, actually decreasing cooling at highway speeds. The solution was to make holes in the corners and put very thin rubber flaps over the holes. That allowed the fan to pull air through the whole radiator when stopped or in slow traffic because the flaps are closed and also full air flow through the radiator a higher speeds when the flaps are pushed open removing the dead spots in the corners.
