Harry potter hen help!

Hi all! I'm attending a harry potter themed hen night out. The brief for outfit is quite loose - either choose your house and dress in those colours, or go with the school uniform/hogwarts look (but glammed up, short skirt etc).

I'm not a big harry potter fan so funny wanna buy clothing I'm not going to wear again, and don't have a grey skirt/white shirt already.

I DO have a short burgundy shift type dress - plain but fairly glam looking- that though is a bit darker in colour I I might be able to get away with if I go gryffindor colours?

Any ideas welcome for what to pair with it! A tie? Though without a collar will that look silly? A yellow-gold hair bow? I've picked up a HP wand cheaply to carry also.