Hi Mark
Welcome to the JY Forum. All of us were newbies at one time so understand the nervousness. As part of a JY group on a trip you will only be alone if you want to be - obviously you need to get to your departure airport but once there look for the JY luggage tags and you will have made friends before you leave the UK.
I assume you know where you want to go so you will have the destination in common with the other travellers in your group. Go for it - all you have to lose is a few days out of your life, some money but experience is never cheap. What you have to gain is a world of travel and lots of new friends and experiences.