This happened a week ago. I'm kind of feeling anxious about this even though my friends reassured me I did nothing wrong. I just wanted reddits opinion. 

Last week, my friend (Rob) and I visited Victoria, B.C., and we came back to Vancouver on a ferry that was absolutely full. It was the most popular crossing time back home and throughout the duration of the crossing, the steward kept making announcements to please remove jackets and bags from seats because people have no where to sit. Stupidly, my friend and I decided to eat before finding a seat. Once we were done, we walked around the ferry, all levels, trying to get a seat with no luck. Finally, we came across a row of seats that were empty, with 2 books taking up seats right in the middle. In my brain, this meant that those 2 middle seats are "reserved" by someone, so my friend and I took the seats on the sides (aisle and window). We both thought this would be fine, as we left the "reserved" seats empty. 20 minutes later, a couple comes by. I was reading, Rob was sleeping. I heard them talk (not English) so I looked up at them and then they asked me why we took their seats. I haaaate confrontation as I have pretty bad social anxiety. I politely told them that my friend and I were looking for seats and we took the 2 that were empty. They are welcome to return to the 2 seats they reserved. Then they told me that they had in fact reserved all 4 seats and that their friends are coming back. I apologized again, but I said I wouldn't move because:
1. Only 2 of 4 seats were "reserved". 
2. There were 4 people in their party, they couldve left someone behind to guard their seats. They brought their food and drink over to the seats so it's not like they just went to eat in the cafeteria area of the ferry. They were going to eat in their seats. 
3. Rob and I walked over 20km that day, I wasn't going to walk all over the damn ferry again. It was too cold to sit outside. 

I would appreciate your opinion. 

Sorry for the wall of text, am on mobile. 

