If it's a used latch, it's very possible that it's distorted from use. Only thing for it that I know is to fiddle with it, bending it here and there (usually the lower half I think?) or filling the gaps with larger material until you're happy.
I've done both over the years, and was generally getting the results I expected, but if you ask anyone who's run a stock carrier for very long, they'll most likely tell you that it's never going to be perfect. Mine worked as well as I expected, but I spent years trying to find a suitable replacement with better latch (like off the later 90's Broncos) or a new design like on a bumper.
I eventually went with an on-bumper carrier.
Paul