Your concerns are perfectly normal.
Do at all times remember that you had an interview, and you did get hired. If you were bad at what you do, why would you have gotten the job? They clearly believe you're as good as the impression you left. If you exaggerated a lot during your interview, this might be a little problem. However, if you told them the truth, you will only have to continue being yourself.
If you do not know something, ask! If you make a mistake, acknowledge this and ask for advise on how you can avoid making such mistake again. It will be appreciated, by your employer and by your colleagues.
When I first started working where I now work, I used to break our development server every week. When the server showed odd behaviour, everyone jokingly pointed at me. Do not take things like this personally! Now, after 18 months, I rarely break the development server and now I can point at others when it breaks down; it feels great.
In short, the only thing that you should worry about is the asking of questions. When everyone talks about bytecode manipulation and you don't know what they're talking about, it might indeed be difficult to stop them in their conversation to ask for a brief overview of the subject. However, not asking at all (and thus not joining the discussion) is much, much, much worse.
Acknowledge that you're not a professional, and show that you're eager to learn.