The former Watford boss praised his players for getting to the final on May 18, but stressed their mission is not yet complete.
Boothroyd said: "Getting to Wembley is an achievement but it's only an achievement if you can finish the job off.
"It's a job that has got one more game to go. At the start of the season we set out to try and win promotion and now we've got an opportunity to achieve that in a one-off game.
"There are two things that are going to happen next Saturday, there is going to be an occasion and there is going to be a game and we've got to make sure that we play the game."