I was extremely nervous before doing boxing, mma, and bjj. The thing is, it isn't a competition and nobody is going to care if you are further behind. In a good gym, people will be extremely helpful and everyone there is there for the same reason as you, to learn.
When I started BJJ, I was way behind the others there, and I got tapped on a regular basis, but I learned so much. They will usually help you if you ask for help, and nobody is going to rag on you for not being as good as them.
Trust me, once you get in there, you will see how much fun it is and you will forget about being nervous and begin to look forward to training!
"We are the children of your rivals,
Sig Credit: M.C
Holding guns while reading Bibles."