Actually...

The word "actually" generally relates the sentence that follows it to something that has been said recently, generally either to clarify or contradict. So when you say "Actually, yoga class might be pretty empty tonight", it doesn't really work, because I am certain that we have not spoken about your yoga class today. I'm certain of this because I know I would never have started that conversation, and if you had started that conversation, I would have pretended to be listening to my invisible Ipod.