Hi Caz, feeling nervous is normal, everyone feels the same! I took forever before deciding to book a trip, but once I was on it and met everyone it was fine, you soon forget about feeling alone as everyones in the same position. I've only done a few trips and still feel nervous before booking, but do it once and it does get easier.
just be yourself and don't be afraid to chat to everyone, my experience is that everyone is friendly and its great to meet new people and share different experiences, good luck on your trip!