I think now I got it. I have a TabHost, in one tab I put a scrollview. In another layout I have the views, filled by using %y in the Designer script. I want to fill the whole screen but I don't know the resolution.
then, before loading the layout to the scrollview, setting Scrollview.Panel.Height to 95%y (because tabhost occupies a part of the screen) it fits OK.
So, why use a TabHost? because I want to see similar size of views when you rotate the screen, forcing that horizontally has the same height as vertically.
Finally, I use this:
If Activity.Height > Activity.Width Then
ScrollView1.Panel.Height = 95%y
Else
ScrollView1.Panel.Height = 95%x
End If
I'm sure there is a better way to do this, but it seems to work.