Higher Maths with a D in National 5 best approach

Hello to all, I have just completed a work experience placement and one of the things I have now learnt is that to take a graduate apprenticeship at uni, I will need to take higher maths. However, I am currently taking applications of maths and have already missed a few months of work and as mentioned in the title, I have only got a D in nat 5, for whatever that reason is I am not sure, maybe lack of studying throughout the year but regardless I am going off the assumption they would let me take higher maths. To be clear, assuming that I get accepted at the workplace, I would automatically be accepted in uni with even a C at higher maths. So I don't really have a exact question, just any advice at all would be great. Ideally leaving this year was the ideal scenario but of course this may not be the case anymore which I am a bit gutted for. Thanks in advance for your responses.