Beauty and the Beast backpack

Okay so I have this beauty and the beast backpack and I'm planning to take it to school and I usually don't care what people care about me since I don't talk to many people but I put a picture of the backpack on my Snapchat and someone that I'm really close to who just graduated from that school asked me if it was for school and I replied yes it was and she told me no and to not do it. In my opinion the backpack doesn't really look childish or anything and when I asked her why she never replied but just read it. I honestly have no idea what might be wrong with the backpack and because it came from someone I've opened up to in a way it's making me paranoid, especially since they won't answer why I shouldn't take it. What do you guys think? I'm going to be a sophomore by the way.