Baffled by fusion 360 - need help :-)

[Britannicus]

I think this should be a simple 3d shape to cut - a simple flat triangle with a 72deg chamfer on 2 edges - the idea is to cut 5 which will then be stuck together to make a pentagon pyramid.

the whole thing is quite small (25 mm from base to point) and I'm using a 1mm flat bit - I went for a 3d contour and it generates to toolpaths except for 2 very annoying things.

I selected 3d contour and used the top and bottom contours to cut to

the cut doesn't go all the way down to the bottom contour

It won't cut along the vertical (short side) -I've tried using other modes with the same result

I'm clearly setting something wrong in using contour (I've only used it in 2d mode before) - can anyone help me with what I'm dong wrong ??