I'm drawing a basic ribbon. I have a triangle for the fold of the ribbon.
My problem is that despite the anchor points being in the correct position, the points of the stroke (top right and bottom left) are over-extending.
How can I fix this?
That behaviour is controlled by the details of the Stroke Palette, and you can switch how the stroke is aligned to the vector spline beneath - centred, edge-in, edge-out, and you also get control of corner behaviours there too: rounded, mitred or beveled. I kept a centre alignment and went with a rounded corner, knowing the other corner from the rectangle would provide the needed visual cues.
Hope that helps.