Crossfit is intimidating in the beginning. I think I had an advantage because the class I started in was the 5:30 am class and only had 2-3 other people, who were very encouraging and the coach had the time to give me extra guidance. (Since then, the box has grown and the class size tripled and quadrupled.) I did Crossfit for months before I ever RX'd one and it has been a while since I've RX'd another one. Those are goals to work towards and you should not feel like you should RX ever single thing. You are competing against yourself and you should not feel like you have to be an expert at it when you are so new.
The WOD is designed to push you, but you should not feel bad about scaling a WOD. I have been Crossfitting since July and I am just now able to do 1-2 pull-ups, still can't do a ring-dip, and don't even ask about my double-unders.... LOL I have improved in many areas and I hope to RX more WODs, but I don't want to hurt or injure myself. The key is to have fun, make some friends and improve over time. Crossfit should make you feel good. If it doesn't, maybe it isn't your thing. There's nothing wrong with that. I wasn't sure it would be my thing at first either. (BTW, I'm a 40 year old female and this is the first workout stuff I've EVER done.)