A fourth A level would help you get into one of the more prestigious universities. They would probably ask for at least three A-levels in traditional subjects. Maths and physics counts but 3D design does not. So it depends on if you do go to uni and if so, which uni you go to. Have you looked at possible courses on the UCAS website and their entry requirements? If not, worth a go, even if you're not sure what you'd do. Computer science is an obvious possibility from what you've said, as well as maths, physics and one of the engineering subjects.
Studying on your own is possible but probably very hard. You're much better off having some kind of tuition. Could you possibly enrol at another A-level college? I assume you would not be able to get a private tutor.