I just did my first solo cruise, although I'm not sure if I would have been so brave had it been my first cruise AND first time solo.
As others have said, you should get involved. Even though this was my first totally solo cruise, in the past my girls would bring their friends and I'd spend most of my time alone anyway.
My last cruise I went by myself for two weeks. I didn't feel lonely at all. We had great table mates, and they would invite me to go to shows or the lounges with them in the evening. I found others traveling alone, and we'd meet for shore excursions and share cabs and such. It seems to be easy to meet others on a cruise, because so much is done (sharing style). I can't think of any other type of 'restaurant" where they seat total strangers at your table. You really do get to know your dinner table mates.
I also managed to meet new people every day during other meals because if you are sitting by yourself, and if the tables become scarce, others will ask if they can sit with you and strike up a conversation.
I always book inside cabins because I hardly ever spend time in my cabin anyway, and I enjoy spending money on something else. Others really enjoy the outside cabins and would have it no other way. It's a matter of preference, but nothing at all wrong with an inside. I find having an inside cabin makes me go outside more, as I can't just look out a window if I want a view. LOL