Everyone is nervous about this, so you should just say it at the beginning of your talk. Don't be afraid to take a break, you're the only one who "hears" the awkward silence. Taking a break is good, drinking some water etc. Smile. Choose one person in the audience, preferrable someone you trust or someone who is kind to you, and look at him/her throughout the entire presentation (look a bit at the lecturer too). I hope it goes well!