I know, I know. As an editor, I know from plenty of experience that there are always a few errors that get thru, particularly in longer pieces.
I think you can still go in and change it. Just click "Edit," which is right beside "Reply" at the bottom of your post.
That "Edit" function is available for 7 days after posting, but at the end of the 7th day, the post will be permanently recorded as is on the blockchain.