I also did this last year!
I believe I got around 168/175 so A^/A**
We were put into sets for GCSE maths and the top two sets just integrated the FM spec into the year so I actually still have no idea what topics were on the normal maths GCSE and which were only on FM!
Honestly I didn’t find it much harder than normal maths (probably for that reason!) but practise makes perfect!