Hey there!
I want to design a 3d printing part for the dashboard of my golf 6, more precisely the top middle part right 
.
I am somewhat experienced with designing parts in fusion 360 for daily usage, but I don't really know how to design this part.
I did try getting a fit for the front arc and an arc from the middle front to the middle back, then did construct a plane from both arcs and did round the result on both back edges. But I noticed when trying the fit, that the dashboard top is not really symmetric, but has an additional bump to the left.
Do you have any tips/guidance/ideas on how to get a better fit? I did think about scanning it 3d with some lidar device, but I don't have an iPhone and wouldn't know where else to get a device.
Probably without a 3d scanner, using paper and scissor you will only get a (hopefully) better and better approximation of the real surface.
Anyway, without a 3d scanner, to have some precise measurement you could just use some modeling clay to recreate the correct form and then set some reference point and take measurements from there, it should be precise enough to create a model in Fusion360 that account also for every asymmetry that could be present.
I'm now trying to maybe get an iphone from a friend and test out the 3d scanning of that device. but yeah, i also feel like modeling clay is my best shot.