I am a 30 year old female that was in the same situation as you, trying to get my friend to come with me. Finally, I just decided to book what I wanted to do, and if she decided to come along, great, but if not, I was still going to go. It's my first vacation by myself, so I'm nervous about that. I'm also nervous about the sharing a room with a stranger, but keeping my fingers crossed. I would reccommend at least putting a deposit down right away. I called them last week and they already had 225 or so people booked. In August, they will be opening up a message board for those of us who are signed up.
Hopefully, see you on board.