I want an Untrimmed surface!!

When I create a set of points and connect them using the interpolate component then I use the surface parameter, the output is a "Trimmed Surface" (You can read it by hovering over the Surface Parameter. Why is that happening? I didn't trim anything!!! I want it to be "Untrimmed Surface" because I am going to use the Region Union Component to combine it with other surfaces and that component does not recognize Trimmed Surfaces! What to do?? Is there a way I can draw Untrimmed Surfaces using the spline curves?