1. Everyone feels a bit nervous about meeting new people.
The only way to overcome this is practice. The day of the meetup I tried to take my mind off it by organising other errands before it so as I wouldn't sabotage myself.
2. There will probably be other beginners there.
I certainly felt out of my dept at many points but there was no expectation that I should do anything except for listen and learn. The option was there to ask questions, or contribute but most people who were there for the first time did not.
3. The worst that can happen is you decided its not for you, make your excuses and leave.
This is highly unlikely but a good thing to tell yourself if you start to consider cancelling on the event.
4. You'll probably be glad you went.
Even if you learn nothing, which is unlikely, you will be glad that you have pushed yourself. It's more likely that you will make new contacts, learn something about programming and remove all the false assumptions you may have made before going. For those reasons alone, it really is worth trying.