The script code doesn't need to change at all, The problem is in how your HTML code is structured.
When scrollable looks around for your prev/next buttons, it goes to the parent of div.scrollable and checks there. On your current page design, that means it searches div.full which contains all three. That's why you're experiencing your problem.
The solution is to wrap each prev/scrollable/next section inside their own container, so that scrollable will only find the one appropriate prev/next when it goes searching for them.
<a class="prev browse left"></a>
<!-- content here -->
<a class="next browse right"></a>