Thanks for playing!
I think I should have made it a bit clearer that you have to press A to choose a quest from the missing poster board, then get on the horse to start the level. Sounds like you hadn't picked a quest in your playthrough?
I also don't like how it's B to look at the poster, but A to select a quest, especially when playing on a keyboard instead of a controller, so I might play around with these controls in future to make it a bit clearer.