Go onto your listing in hosting mode and under the Listing Editor on your left, click on Availability and alter the maximum trip length on your right and press save
Your listing looks like it is in a really quiet and peaceful spot, guests must have a lovely time unwinding there!
In regards to your availability settings, have you had a chance to try out Joelle's advice? It would be great to know if it helped or if you need a little more guidance. 🙂