You need to be a bit more specific in terms of computers. Because computers could mean coding and developing programs which you want to probably do computer science or software engineering in university, which from what I know from friends who are doing those degrees requires like extension 1 math because you have to do math subjects in uni. However, an interest in computers could also just mean like building them or working on them in a shop where you fix it, which you don't really need uni for since you could just learn that from tafe or some skills based school
I think more importantly though is you need to probably evaluate your study habits because getting the kind of grades you are getting indicates you are not studying as much as you should be, rather than solely indicating you are just poor at the subject. This is because with effort and consistent studying most people can get around 70-80% even if they are not good at the subject naturally
