Click where you want it to be. Switch to the Front view to move the arrow on the ellipse. It should now look like the image below. Then click where you want it to be. Click on the Rebuild button and put 30 in the control points.
Lets take a look at it and see how smooth the surface looks.
Click on the surface you just made. Rotate your view and see how smooth it looks. You can do this as many times as you want, but it's better not to, as it will deform your shape as it smoothes it. Lets hide the curves we used to make this surface to get them out of the way. Make sure you have your surface selected.