You should do a degree because you're interested in the subject. There is plenty of research that demonstrates that people who do non-vocational degrees end up doing better in career terms than those who choose purely vocational subjects.
Good degrees teach you how to think; subject specialism is secondary.
Very, very few degrees lead straight into a job: even some of the old guard vocational ones require further training (medicine, law for example)
The world and McDonalds are indeed littered with people not using their degrees but this has precious little to do with the subject they studied.
Employers are not looking for people with vocational knowledge (unless it's a nursing degree for example) - they prefer to do the vocational training themselves. What they are looking for in graduates is bright, educated people who know how to solve problems, work with others, find information, make good judgements. A good degree in English, Sociology, Philosophy, History, Psychology, French, Chemistry or whatever can give you these things.
The danger of trying to tailor a long and difficult learning plan to what job you want and what salary you need is you end up choosing something you hate and do badly at: it is far worse to have a poor (pass or third class) than it is to have a 2.1 in something non-vocational.
Graduates earn more than the wider population at large for all the above reasons and more. Psychology is a great basis for many careers (eg in social care, in HR, in management, in teaching, in social and voluntary work, in clinical psychology).
If you need any more advice about degrees or applying to university please just ask!