In my experience, people tend to be really friendly on a cruise. Don't hesitate to do anything on the schedule that looks fun. We've had others join our team for trivia or share a table with us at the cooking demonstrations and alcohol tastings (mixology, wine tasting, etc.). I often go to activities alone when my family is off doing other things or isn't interested in that event. It's never been an issue.
Don't forget that the movie theater shows first-run Disney company films so that's always a great way to spend a couple of hours. Also, there is usually a Single Cruisers lunch and other get togethers throughout the cruise.
Finally, you can join the thread for your sail date in the Cruise Meets section of this board (at the top of the main page). Perhaps there are other single cruisers there. They may also be planning group activities in which you could participate.
Have a great time!