All tickets are return tickets. This means that the ticket is valid for a trip out and a return trip. This applies no matter where you decide to get off (Munke Mose, Odense Zoo or Fruens Bøge).
You can therefore get off at Odense Zoo or Fruens Bøge and use the same ticket for the return trip. When you book a trip, you can choose the departure time and the return time, so that you are ensured a seat at the boat.