You should have returned it for another one. If there are any blemishes on a new razor that's a manufacturers defect. If it was rust it wasn't stored or protected. Either way you should have sent it back.

Of course now that you messed with it your stuck. If its a blemish from a vise or something I don't know you can fix it unless you have a dremmel and polish it out or use some sandpaper to get it out. otherwise can you live with it?