I used to lecture to 70+ students at a time and very daunting at first. But prep, structuring your talk and of course knowing your subject and practicing are key and ultimately increase confidence. Try to get into that zone where you’re talking to a group of friends, not strangers. Definitely try to engage and build rapport, not just talk at them. In the past I’ve started with a question related to the topic to weave into the intro too. Means some of the audience engages first and can relax the atmosphere.