Correctable Error?

[qcumpire]

This situation occured last night.

High school game using Fed rule book.

Within the last minute of the half, offensive team is out of timeouts. First down the ball carrier is pulled down in the backfield (the previous play the offense had converted a fourth down situation). The referee stops the clock after the first down play and emphatically sells a first down for the defense. The only problem was, he forgot it was not fourth down any more.

At least ten seconds passed before the referee realizes his error and re-starts the clock. In that time the offense is able to line up and is ready to run the next play.

My question is: Since the Referee knew he made a mistake by stopping the clock (He admitted it to the defensive coach after second down), is this a correctable error, and could he take time off the clock?