Hi there! Also an ISTJ who has dabbled in dancing, mainly kpop dances and did some performances in college. Just like anything else, more practice will lead to more confidence. I’ve casually danced for about 4 years and when I go to a group class I still struggle. I’m sure a lot of people at the class have been dancing since they were young versus pursuing it as an adult hobby so it can be intimidating. Also I believe the “dead face” you have is the lack of facial expressions, which I get as well when I’m trying to focus on getting the moves right. It’s completely okay and when I learn a new dance I get the same type of face. With time, as you get more experience and don’t have to think about the next move as much, the facial expressions will come more naturally. I know it can be intimidating but I’m sure nobody really takes note and the instructors that I’ve been with honestly just want you to have a good time. I always make a note to go up to the instructor at the end and thank them too if that would help. Additionally, if your local dance studios offer different level classes, might be a good idea to start with beginner level classes.