Thanks for the fast reply.
I should have given some context. In semester 1, I failed a core subject because I missed out on the obligatory classes twice... Yeah I really screwed up 
Come results time and I get a fail. It was removed from my study plan so I thought I could make up for the missing credit this semester because it's my last year and I want to graduate.
Do you know if they would give permission in such a case? Do I need to book one of those online appointments, I've never been to the centre.
No probs, but is there a reason why you have to do 5 subjects? E.g. if you were doing a bsc couldn't you just swap your breadth for a science this sem or drop a science elective? It would just reduce the workload so much (and you wouldn't have to worry about persuading them to allow you to overload).
So if it's one of those subjects offered in both sem 1 and sem 2, you should be able to complete it for sem 2. Best to get in contact with the coordinator for the subject in that case (details of their email on the handbook etc.) and if they give their approval, forward that email to the student centre and they should be able to manually enrol the subject on your study plan for you. Keep in mind that classes may be full so you should go to the student centre in that case.
Edit: I just noticed you saying you were in your last year. Is one of your bachelor's subjects simply an elective and not contributing to your major or are they all prereqs?