Hi thisisfine, Going back to school and having a new baby in the house is reason to feel some stress. Try to think of the good things You are going to be a big sister! That is awesome! Congratulations!
I also suggest trying to stay in the moment school hasn't started yet and the baby is not here yet, just live day to day, you can't do anything about what hasn't happened. Look at it as a good experience. We are here for you.