What chance do I have of becoming an academic (of psychology)?

Sheffield Hallam University has an excellent Psychology Department and often require slightly lower grades although I am not sure exactly what they are. These are only your AS grades and you could improve on these in the actual A Level - you may well be able to re-sit a couple of AS modules to achieve that. Ask your teacher when you return to school. There is no reason why you shouldn't become an academic if that's what you want, but a degree in, for example, Psychology will open all sorts of doors. Good luck.