had a quick look at your capx..
the main issue i can see with the scrolling issue is your events in the scroll group
using the viewport as the base is restricting the scroll...because even though the layout is bigger..the viewport size is fixed..
so if you use that value ..it will always stop at the viewport x distance and go no further
does that make sense?
tried a little fix for the scrolling in your capx and commented my changes...
the spawning issue is more complex because based on what I can see...you want different distances between each spawned ground block
you would need to alter the spawning to take into consideration the position of the last ground block and a random range of values to add to the new x spawn position.
I didnt change this because you may have other ideas for generating distances (a formula of increases perhaps)
hope that helps alittle