I get lost with equations pretty easy. So let’s start over.
If you have 4 points: A, B, C, D
You can make a curve through it where it ends on points A and D and the control points are B and C, but they won’t be on the curve.
So something like this to get the points to to draw the curve along.
Repeat 10 times
— set x to cubic(ax,bx,cx,dx, loopindex/10)
— set y to cubic(ay,by,cy,dy, loopindex/10