It's one thing getting an 'A' in AS Mathematics and then another to get around a B in A2 Further Mathematics though. However, that said, dropping Biology and ICT would give you the platform to study A2 Further Mathematics.
The thing is, iirc, A2 Further Mathematics made up of 6 modules, as is A2 Mathematics; I would be suprised if you would then effectively have to do 9 modules of maths next year (including the 6 of Further and 3 of Maths), as you would have to get up to AS standard (and cover the whole course) as well in Further Mathematics, if that makes sense. It goes without saying, that the 'fast track' Further Mathematics would require a heck of a lot of work.
If you come out of year 13 with good grades, then the step up to a university degree would be 'managable'.