I always feel left out! How can I fit in more?

First, stop with the competition thinking. You are there because you enjoy it, right? If they are making inside jokes, are you sure you want to be a part of that? To be as good as them will take time but you will only be as good as you want to be. Practise, practise and more practise, just like every thing else and remember, no matter how good you are, there will always be someone just a little bit better out there. It's the same with anything, so again do it for you and have fun!