More proof that a picture is worth a thousand words. Both the problem and solution are now obvious.
The problem is the rust, and the post will fit perfectly with a light sanding to remove it. Or replace it with an aluminum 27.2 post.
BTW - be careful and do not overnighter the clamp. The ears seem to be bent inward, probably from overtightening in the past. Keep it up and you might Crack the tube, or bend them in enough to touch.
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