Firstly, History is not pointless, in fact you do a history paper in your first year, and if you have studies some of the topics (such as Industrial Revolution) at A Level it would definitely aid you. It also provides a solid essay-writing background, which is essential when you are writing 16 essays a term.
Secondly, Further Maths is a HUGE advantage. Not least because the course here is really very mathematical. First year maths does go beyond the further maths syllabus (slightly) and the course really does move at some pace, so keeping up without further maths is more difficult. Also, given the number of people who really struggle with second year maths, FM is the best indication you can give to the college that you can definitely handle it.
Just as an indication, I can think of perhaps 3 or 4 people who i have spoken to in lectures who have not done FM. in my college, out of 7 of us, 6 have done FM. It's not so much that you are at a slight disadvantge without it, more that you are at a significant advantage with FM. You have to understand just how competitive Econ at cam it to get in for. You need to differentiate yourself from the average applicant as much as possible.
I know this may not help you that much now, seeing as we are already 3 months into the academic year, but to anyone else who is a year behind you, hopefully they will gain something from this.