Am I making a mistake?

Grade requirements are about 'positioning'. Unis set the grades as a) what they think will get the the right applicants but not be too off putting that they can still fill the course and b) doesnt make them look 'lower' than what they percieve as parallel Unis. Non-London Unis tend to have lower entry requirements - not because they are rubbish but because London seems more glamorous and London Unis therefore get more applications - so KCL, LSE, UCL etc set their entry requirements higher as a form of filter and because they can afford to be more selective.

So - AAA, AAB or whatever doesnt tell you anything about the 'quality' of the course and it certainly wont tell you if you will like the Uni or enjoy that course. If the course/Uni is what you want then go for it - you are not 'under-selling' yourself, you are making a sensible decision about which Uni or course will suit you and which you will enjoy doing. Nottingham, as just one example, is a top Uni and well regarded by employers - it just isnt 'in London'. Go where you will feel happy because that IS what matters.

So I applied for law last year and got offers from some really good universities but I decided not to accept any as I realised I was just doing it as it is a prestigious degree and can make a lot of money, rather than being something I’m genuinely interested in.is that for
This year I am thinking of applying to finance/business/economics courses, as that’s where my passion actually lies.
My a level grades are A*AA (with A* in epq) and I am wondering if people think I’m ‘wasting’ my grades applying for courses with AAA or AAB requirements. For example I love the look of the finance, accounting and management course at Nottingham. I went to the open day and I’m genuinely interested and think I could do really well in the degree, but the requirements are AAB.
I know it sounds stupid but I don’t know if I’m wasting my potential by choosing a less prestigious course with lower requirements just because it interests me?
Any opinions would be really appreciated

Nottingham is a great university and would be fine. The only problem I can foresee is that for some of your courses there might be a Maths requirement. Check that you meet that requiremen. If you later decide to be a solicitor or barrister you could do a converion course which many do.