I went on my first solo cruise (Carnival Freedom) in November 2013 and had the same concerns as you. I had a blast! I just booked my my second solo cruise today...Carnival Splendor, NYC-Bahamas on April 2, 2014...Anyone else going? As Carnival offers the no supplement on so many cruises, you will meet a lot of other singles too.
I just really like being on my own, doing what I want when I want etc.... I met so many nice people. I think more so than if I was with someone else. I had more people offer me to join them at their table or join them on their port excursions. I think I can sum it all up by saying I was alone when I wanted to be and never felt lonely...and found friends when I wanted to socialize. I suggest you go for it and have fun!
Don't forget the sunscreen!