How do you page through entries in a structure?
Craft provides many helpful methods to traverse structure sections and your use case is no exception.

Instead of using .getPrev() or .getNext(), try .getPrevSibling() or .getNextSibling() (or their aliases .prevSibling and .nextSibling.)

You could create prev/next links with something like this:

{% set prev = entry.prevSibling %}
{% if prev %}
    &lt;a href="{{ prev.url }}"&gt;{{ prev.title }}&lt;/a&gt;
{% endif %}

{% set next = entry.nextSibling %}
{% if next %}
    &lt;a href="{{ next.url }}"&gt;{{ next.title }}&lt;/a&gt;
{% endif %}