Let us know what happens, I think you deserve a refund, 30 miles or no. Keep that in mind, and if they won't do it ask to speak to manager or something. It's ridiculous you ended up with a bike too big for you.

I'm 5'4, I ride a 52cm (fitted) and a 53cm (not fitted, used junker bike). I don't have any standover clearance on either one, and they both fit, but I have to wear sneakers with thick soles. That being said, 50cm for your height sounds too big.