Well, it's not too late, though you probably should try to do at least AS Biology next year. And you'll need to arrange work experience for at least your summer holidays.
Though with a maths degree, on paper, if anything, it shows that you've got brains, not to mention you'd be employable in the financial sector, in maths degrees you'd even be able to study quantum physics, so that's another path you might want to explore. Besides, maths is such an interesting degree as well, if I'm not applying for engineering, maths would've been my choice. I mean, if you're more interested in and attracted to maths than all other subjects, go for maths, it's not like some kind of study of pre-historic rock formation or the research into the evolution of maps.
If you really want a highly employable degree for uni, you can also go for one of the many varieties of engineering, and I only really realised that engineering was for me (in terms of job prospects and degree content) at around the end of my AS year anyway.
Though talking to my friends, apparently the veterinarians are relatively underpaid, much less than doctors i think.
And: I'm doing the same A levels as you, just took them all to A2