I'm not certain you've actually done anything wrong. Your son's app should cost the same as your own, and the details required are basically identical. Tell the courier to write on the form that he is applying as your dependant, which is obvious anyway, and to submit what you've given her. Your only other option would be to complete and pay for the other application, then ask for a refund for the first one. But again....and I'm not an expert of course....I am not sure that you need to change anything.