I am currently pursuing BBA from a private institute. But I didn't clear one paper in my 12th exam, and somehow I joined this course in this institute. Just wanted to know, if this will be considered a valid degree or not?

In case not, can I write that particular 12th paper again? Or do I have to write all the papers again? Before that, can I appear in 12th exam again, as it has been few years when I gave my 12th papers. If yes, will my current degree be considered valid if I clear the papers now, or will I have to do this course again, from beginning?