Chief, I'm relieved to find that you are not a chump! Here's a quote from the USGA rules webpage:
"Q. A player, unable to find his ball, puts another ball into play. He then discovers that his original ball is in the hole. What is the ruling?
A. The score with the original ball counts. The play of the hole was completed when the player holed that ball."
Sorry to take so long, posts on the rules forum don't get emailed to me, so I have to remember to look here. Nor are line breaks, is seems.