Firstly - you got 93% on your exam, why on Earth would you want to switch? At my school, that was the highest exam score for unit 1/2, and someone who got under that ended up getting 42 the next year.
Secondly - After scaling, it doesn't matter how well you do in either subject, you'll probably find that how much you do better in Further will come below what your methods would move up to.
Thirdly - Find out what modules your school does - if they do say, matrices and linear relationships, you'll be fine. If they do financial and networks, you might have a bit more trouble. You'll have to learn a bit in core, but given the pace you'll have to learn it, you should be all right.
Finally - I have heard plenty of stories of people who have switched from methods to further and done very well, I wouldn't stress about not doing general maths.