Best of luck to you, but whatever you do, don't drop economics a level in favour of business studies. Anything that ends in "studies" is not an A level worth having.
You don't suggest from your posts that you are great at maths. You do realise that an economics degree (a finance degree is a watered-down economics degree, barely worth doing) is difficult applied maths right? And that an economics degree is the best way into finance (maths, physics and chemistry being the other good degrees) a watered-down "finance studies" course won't get you as far as you are hoping.
Sorry, but physics and chemistry being better routes into finance than accounting or business finance? Oh, you're 21.