If its not possible for you to make any sort of non overlapping timetable then they may squeeze you into an already full lecture/tutorial, happend to me. To do that though you'll need to physically go to the relevant school on campus.
if there are no more places left in the particular subjects, does that mean a commerce or economics student who needs this subject will need to withdraw from the course since they cannot do the subject? or does the uni open another class?