How to hide a D on CV

Most jobs will not ask for a uni transcript only the overall classification except maybe certain internships and big companies, but even the ones that ask for it they won’t analyse every detail of your transcript. They maybe glance at it for 2 seconds or not even look at it and focus on your CV (which you do not need to mention it in at all in your CV). If you think about it they’ll probably have hundreds of applicants so they won’t spend ages analysing everyone’s transcripts.
Also a subject like maths I would think is not super important in journalism, it’s not like you’re applying to be a rocket scientist. Maybe some basic maths, but like you say if you have GCSE or a level maths that should be plenty for journalism.
What matters most is your cover letter and Cv I’d say. You don’t have to mention anything you don’t want to in a Cv. Just make sure you have a strong Cv stating all your good skills, why you want the job and what you think you could bring to the company etc...

Also I’m not entirely sure what you mean by you were meant to have passed... do you mean you were meant to have passed maths? Passed the year? How much this matters would depend on your uni. Is passing this subject important for you progressing to next year? At my uni I failed one module in 1st year but it didn’t matter as I had enough credits. Whereas my friend also failed a module but did not have enough credits so had to resist 1st year. So you may want to check with your teacher/ supervisor about that to make sure everything is on track.