Unfortunately, you're probably right. Trip Delay usually has a clause that you have to be delayed more that X number of hours. Some 4, some 12, some more. Trip Interruption usually has a clause whereas you are required to do everything possible to get to your destination (and in the case of a cruise, catch up at a distant port). Again, unfortunately, you took the word of a cruise line agent and stopped your trip without first calling the insurance company for their advice and/or consent.
You may be royally screwed, but there are many lessons in your story for others to learn from.
* Cruise line air - Don't buy the marketing literature. What is in the legal documents?
* Trust but verify - When in a jam, call the TA or cruise line for advice, but also call the travel insurance company so they can advise. They may agree with previous advice, but they can also advise what documents you may need to help your case. (I was denied a medical claim once because I didn't notify the insurance company prior to going to the hospital. I knew I needed to do that but my mind was a jumbled mess during the emergency that I forgot. However, that's on me)
Good luck with your FCC from the cruise line.