You can scale a curve along three axes.
Click Modification 
Select the curve.
Click Affinity
.
A 3D box appears around the selection.
Click the curve to position the manipulators depending on the mouse cursor position.
Move the mouse cursor to highlight the desired axis.
Release the left-mouse button when you are satisfied with
the new position of the surface.
Press the Ctrl key.
Hold the left-mouse button and move the mouse to affine the
elements.
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Release the left-mouse button when you are satisfied with
the new position of the surface.