what to wear???

I hope everyone is having a great weekend. I just RSVPed (is that a word?) to a welcome reception for school. The dean and the director of the program are going to be there. So, now I am sitting at work trying to decide what to wear. I know it should be something business casual. But should I go with slacks and a button-up shirt or with a dress? I do not want to be too dressy but I do not want to be under dressed either. I really want to make a good impression, because my program is all about networking and connections. I am hoping to get a really good internship, and it would be great to have the dean and director as close connections. I know I am over-thinking this but I am crazy that way!