One of the bits of advice floating around for scientists is, "Don't apologize for your work". Usually this advice is dispensed within the context of giving a presentation - don't start a presentation with, "Sorry", don't apologize for unreadable graphs, etc.
But I think this advice should be extended to all professional scientific communication. If you hurt someone's feelings or spill their coffee, absolutely you should apologize. Of course you should speak considerately and professionally to all people. But when it comes to communicating science don't apologize for yourself. Don't degrade your expertise, don't qualify your statements.1
You can qualify presentations of information, for example, "This work is preliminary" or "This was just a first step to exploring this problem area." But that is very different from saying, "I realize I am only a masters student" or "Sorry, I am a n00b here" or "I know my undergraduate degree is in French literature, but..."
Be bold! Yes, you will probably need to wave the white flag sometimes. But don't start out with your flag waving. Start out strong.
1 Unless you work in a country where apologizing is the norm for professional communication, in which case, I'm sorry for this post. ;-)