Am I in the wrong for feeling hurt over this ?

Tomorrow I have a wedding and bringing my girlfriend with , the original plans was to pick her up today after work. I left my whole Friday open for her . Last night she tells me she's going to the city , she has a friend who's in town for one day and she just asked her to go with her . It really bummed me out , like my plans and schedule doesnt matter . She asked me what my plans were and I said she was the plan originally. I explained how I felt and she appolgized for making me feel that way . Yet I still feel bummed even if I'm seeing her tomorrow or possibly late tonight. I don't want to keep her away from her friends, I just don't know how to resolve this feeling or if I'm being too much .