Aftermarket (Curt) Tow Hitch issue

I bought a Curt tow hitch from Amazon. Tried to bolt it on the rear bumper today. The leftmost hole on the bumper does not seem aligned with the other three holes (slightly higher). The Curt hitch slots seem to be level across. It's not a huge difference, but the bolt simply will not go through (despite much wiggling).

Anyone encounter this issue? I'm thinking I may need to grind the one slot a little higher to make it fit.