Sadly a lack of variety can lull an audience into being so passive they switch off. In contrast, if there is variety in a presentation, such as some talking, some audio-visuals, some unexpected activities or other presentation strategies, it helps the audience to pay attention. Doing everything exactly the same way seldom works even for someone with an excellent voice and manner of presentation. For those few who can present successfully for that amount of time without audio-visuals, they are usually very skilled at varying their voice, their timing, their rhythm of speech, their facial expressions and their body movements. Take care of the small details for the audience.
Most people get nervous in front of an audience.
Be kind to yourself. You don't have to be free of nerves to be good - just make sure the nerves don't freeze you. Both Jon and I can still feel nervous in front of an audience. What matters is what you do with the nerves. Don't let them freeze you to the spot - move early and smile early.