Hmmmmm
The Curt website says this, "The 2-1/2" horizontal shank is designed to fit any 2-1/2" x 2-1/2" trailer hitch receiver. This makes it the perfect choice for a CURT Commercial Duty class 5 hitch or other heavy-duty hitches with 2-1/2" receivers.
The shank features rounded edges for easier insertion into the receiver tube, and it has a 5/8" diameter hole to accept a hitch pin or hitch lock for secure mounting in the receiver." (Bolded for emphasis)
https://www2.curtmfg.com/part/17131
I wonder if the one you bought wasn't "completed" ??? The description indicates "rounded edges" which, at least the way I see it (FWIW) yours apparently doesn't ??????