Adjust

CURVEmachine allows you to adjust a few common curve properties, directly from its menu, in edit mode. See the Blender manual for details on the specifics.

Cyclic

enabling cyclicity will close the gap, here on the left side of the spline

Depth

increasing the depth value will create the spline geometry

Extrude

increasing the extrude value will create a flattened spline like this. this example has been tilted too

Resolution

a resolution of 0 produces a square profile, higher values introduce more roundness