How do I limit scrolling position at various levels of zoom

My layout size is 1600,900 and i have a box in the top right corner that is 1280,720 using layer 1(parralex 100), the rest of the screen space is the ui on layer 2 (parralex 0) i've set it up so i can zoom in/out and scroll layer 1,

At the moment after i zoom in I can scroll the 1280,720 box of screen or under the ui, but I want to limit it to its 1280-720 starting position at all the different levels of zoom, any ideas or thoughts would be greatly appreciated

if you looking at the caproj I just want the background to stop scrolling as it gets to the white area.

Thanks in advance

capx - https://app.box.com/s/wlkdlepgauxcmt6x9vdq4b3neo6x3vye

You will need to share a capx, caproj needs all the separate files.

Doh! heres the capx, and thanks for letting me know

capx - https://app.box.com/s/wlkdlepgauxcmt6x9vdq4b3neo6x3vye