I'm having a little difficulty understanding what you mean by the curves are opening, which curves, the original ones you lay down at the base of the skirt or curves that you cross-section on the tutu? The base curves should not open at all since you start with a closed curve.

 

If it’s cross-sectioned curves from the tutu then you need to follow what I said about using the “CrvStart” command and actually window zooming in to see the gaps. I cannot emphasize enough about it not being enough just to blend the curves. They need to be joined solid to the blending curve that is created and the only way to do this is zooming in close. Also, once you’re sure that a curve is closed, save the file and reopen to test it using the loft tool or in the analyze menu click radius and you place it to the curve and move it around the curve you should see a circle moving or if the circle is too big just click on the curve and above the command line if the curve is closed you’ll get a definite radius number feedback if the curve is opened then it will say “radius=infinite” and continue from there. I seem to remember having a similar problem once and thinking that either the computer was screwing up or the software was. Sometimes you might have created more than one curve both occupying the same space (closely occupying the same space), try deleting one and see if one still remains in its place if nothing then undo to bring back the curve. If the cross-sections are bogging you down so much that you’re wasting valuable time then the best thing to do is move on by manually creating your curves.

 

You can lock your main model in the layer’s dialog panel (the little lock next to the light bulb) and build around it looking at your progress from all viewports. Lay down points then connect them to create a curve or you can simply create an ellipse, place it close to where you need the curve and again viewing from all viewports scale it first in the one direction then the other getting the general layout then add control points and pull them out individually to where you need them.