I wonder why the reason for not being able to change the listing or at least  add in some text in the description explaining the error is not possible? 

A lot of people put in a maximum bid or set a snipe when they first see the listing so would not know about the revision and have the chance to withdraw their bid. It would almost certainly lead to a very unhappy buyer and probably neg feedback and rubbish stars.

I would definitely cancel the bid and end the auction, you could email the bidder to explain you are re listing with the revised description, anything else could lead to a not as described case.