ive picked all the core subjects and the one recommended by the course progression map which I think just leaves me with an elective ( correct me if im wrong). How do you know which units are electives and which units aren't?
Elective units are typically any unit from any faculty that you can enrol into that you meet the prerequisites for. When a faculty is attached to 'elective unit' such as 'commerce elective unit', it means it must be a unit taught by the faculty of Business and Economics. Each unit in the handbook has a section in the blue box at the top with 'faculty', and a section below it with the requisites. It is probably easier to browse
Part B in the course handbook I linked earlier. I also recommend reading
Part A: Additional commerce unit and
Part C: Free elective study.
Course maps are flexible granted you plan them correctly to be able to finish on time with the right requirements. For example, you don't have to take the commerce elective unit now that the map recommends, but could swap it with a free elective spot and do the commerce elective later. However, I will again stress it is your responsibility to ensure you're on track and enrolling in the correct units by the time it comes to graduating.
You should have 4 units for semester 1, and 4 units for semester 2 when you submit the unit enrolment.