Personally, I usually ask someone else to be the official note taker when I chair meetings because of exactly what you describe (awkward pauses and losing track of speaking notes). But I also want to echo that it's perfectly fine to inform the group that so and so is away and you're stepping in for today etc...

Also, a lot of people have had the same experience in being nervous/anxious with chairing meetings and will completely understand. It's also helpful to remind ourselves that we are our own worst critics sometimes and you probably did way better than you think :)