Worry but don’t worry.

Worrying about this is good because it will make you better and I think most of the time you should feel like you can’t do the task you’re given without effort, otherwise you’re not challenging yourself enough.

But don’t worry about not being the smartest person in the room at work. It’s an opportunity to learn from great people. Remember that these people you’re impressed by hired you. Personal opinion disclaimer attached, I think many experienced programmers come to realize that how you think and work is way more important than how well you can recite the latest programming trends.

I’d say yes, work hard and practice, but don’t forget to learn from your co-workers too!

I’m in a similar situation where I’m the least experienced of four web developers at a pretty sweet gig.

jdaverin is right, you’re in a good spot where you’re surrounded by people who can make you better, and you’re being challenged by your work. Consider the alternative if you were surrounded by coworkers who have more experience but you find yourself having to clean up after them….

Embrace the opportunity and make the most of it.