Last summer, I traveled through Scandinavia. The plan was to take the overnight ferry from Oslo to Copenhagen, and since I'd been told that the more reasonable cabins sell out quickly, I made my reservation from home about two months before leaving.
On my last scheduled morning in Oslo, planning to sail out at 5PM, I took out my reservation form and discovered that I had made the reservation in the wrong direction, Copenhagen to Oslo instead of Oslo to Copenhagen.
The ferry company's office was within walking distance of my hotel so I went down there to see if there was any way to change my reservation.
There wasn't, and it was too late for a refund. If I really wanted to sail that night, I would have to buy the only option left, a super-duper luxury cabin.
I ended up staying another night in Oslo and taking the train to Copenhagen the next morning. It was cheaper than buying up to the super-duper luxury cabin.