never apologize." The audience doesn't need to know if you're nervous or if you have no experience.
If you're apologizing for not preparing or not having enough time to cover all of your information, you need to keep that to yourself as well. As an audience member, I would feel insulted if you told me these things and I would wonder why you didn't take the time to prepare better, when I'm giving you my time and maybe my money to be there.
Here's a particularly annoying apology/acknowledgement I heard recently on a webinar, after the interviewer took a full five minutes out of an hour presentation to read the speaker's bio.
"Haha, that is one long bio. Thanks for hanging in there."
Maybe it's not exactly an apology, but it's certainly an acknowledgement of a very long bio. If you realize that people are "hanging in there" while your bio is read, then it's too long. Your audience is there for the content, not to learn about your background and degrees in detail.
What are you apologizing for that you shouldn't be doing in the first place?