Making a Tube

In this file:
Forum Tube Question.blend (765.5 KB)

The curve named “Inset” defines the tube’s path. The tube is flat where this Inset curve is horizontal (X axis).

It is desired the tube be just as round as it is when it is vertical to the left and right, along the entire Inset curve.

What has gone wrong here?

your object scale is not 1/1/1, you need to apply the scale. You still won’t have nices corners, so what you need to do is rotate it 90 on the X axis to align it with the XY axis, apply the rotation, then in the Properties panel > Object Data > Shape, choose 2D