HELP with choices please!

I am doing gcses now and i have been entered for further maths gcse but i have been entered very late and the exam is in a month or so and i feel i haven't got enough time to prepare. I have got a conditional offer from Watford grammar school to study Maths, Economics, and History. The a levels have changed now so that you will leave with the AS and therefore come out with 3 and a half a levels even if you started to study 4 subjects, therefore My question is that do you think that the subjects i have chosen along with an EPQ (extended project qualification) ,(which is equivalent to half an a level anyway so i would be coming out with the same amount of a level), is enough to get me into Oxford, Cambridge or LSE. I understand that it is preferred that you do further maths at A level but The sixth form i got the conditional offer from will only allow me to do it if i get an A* in maths and an A* in further maths at GCSE which i am unsure about achieving and it is more unlikely than it is likely. Has anyone here gone to the 3 uni's mentioned with the subjects i have mentioned at A level or anybody knows whether further maths at A level is very necessary to go to the unis i mentioned, i am really freaking out so any advice would be appreciated. I also accept that interviews and the grade you get in the a levels are important but lets just say they went as needed but merely focussing on the subject choices. Thus, which is better, the EPQ in a business related area or an extra A level which is not further maths. Also, does the sixth form you go to matter because i could go to watford grammar and do maths, econ and history and an EPQ or i could go to a less prestigious sixth form Saint dominic's sixth form which would allow me to do maths, econ, further maths and an EPQ. P.S the LSE site says maths is required, economics is ideal, essay based subjects like history and further maths is " a valuable indicator of potential for our highly quantitative degrees", which is what lead me to choose my subjects.