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That's odd. Mine always fit too tight. I used to have a exhaust pipe expander that was made for when you wanted to use a muffler or whatever that had been deformed by a clamp. I wonder if you could expand it with one- or could a exhaust shop do it for you? Good luck!
They sell new/used exhaust pipe expanders should you be interested in owning. Harbor Freight carries them & select automotive supply chains. Here's a used one on eBay: Pittsburgh Tail Pipe Expander, 2-1/8 in. to 3-1/2 in. You might find others.
I straighted it out best I could using a small pipe inside held by a vise, then used lead to fill the small dents and filed it smooth again, like new after painting it..