Ok there are two points.
1. Maths degrees are pretty open. In fact I'd say they're one of the most open degrees you can get. A lot of people think it's either finance or teaching and that's that. But there's also computing/IT, many many other businessy jobs, further research, stats, insurance and accounting and the like, modelling for scientific companies etc etc etc, and on top of that the degree gives you skills which you can apply to mostly anything like civil service or something, as a lot of degrees do. Just be aware of the options. Perhaps email someone at a uni you've applied to's careers dept., they'll probably be happy to advise, or go talk to connexions etc. That can help you check there isn't a route you've missed.
2. What I'd advise is to have a proper deep think now and decide within say, the next month? Perhaps a week before the UCAS deadline or something. Don't be scared about maybe even putting uni off for a year, or asking to change your choice with unis you get an offer at, or similar, because it's much better to do any of that than to end up dropping out part way through because you don't like it, having wasted time and money.
Only thing I'm unsure about is Cambridge, don't know how much you really want to go there and whether you'd have a chance to if you didn't stick with maths now, but at the end of the day you can do great at any university. But of course, you have to factor in this to your decision, if you really want to go there.
Hope you get it sorted out and end up in a degree you enjoy,
xxxx