Should you worry?
No, don't worry. Learn from the experience either way and keep trying if you don't get the job. Eventually you'll get more interviews and eventually you'll get the job from one of those interviewers... unless you quit trying.
Whether you will get the job completely depends on:
- What the question was / how you answered
- The judgement of the interviewer
- Other candidates that are interviewing and how they do
For example it may have been some easy to lookup question that didn't matter, and the interviewer was only looking to see if you could troubleshoot it. In this case it would be good news for you.
On the other hand it could be some easy to look up detail, and the interviewer badly judged that it was important. You probably don't want to work for this company in this case anyway. Interviewers are not perfect either. One may get 100% of the answers correct but the interviewer badly judged that they were correct on one or more answers.
Or it could have been something that was vital to know and you didn't know the answer to it. In either case if the interviewer had good or bad judgement it wouldn't be good news for you on this job in this case.
Keep your spirits up though and keep trying if this one doesn't work out. Learn what you didn't know + more and keep trying. No matter what the job is, knowing more will always give you a higher chance of getting the job.
If you don't get the job it doesn't mean it's from this one wrong answer. There could be a million different reasons including having nothing to do with you.
A good interviewer will see if he can talk you through the right answer eventually. It usually doesn't matter if you get it right on the first try, but that you can easily understand the answer or get to it with some assistance.
It's also a good idea to be willing to, and show the interviewer that you would be very enthusiastic and excited to be working for them. And that you'll work as long as needed to get something done on a tight deadline. If you didn't do this a follow up email will help.