Second baby on the way and have a difficult time.

This will be my second child and I'm going through a really hard time. I don't want my daughter to feel like she's being replaced by the new baby and I just can't seem to get over this. She currently has all of her toys in what will be the nursery and I am transitioning them over to her bedroom. She's only three, so maybe I'm just overthinking things. If you went through this, how did you get through it?