I have only just started reading this thread, but found this page.
http://www.nzta.govt.nz/resources/roadcode/about-driving/giving-way-at-roundabouts/
One of the paragraphs I note in the double lane round about section is:
Not all roundabouts are marked the same way, so take extra care – especially at the exits. If you need to cross from one lane to another near an exit, give way to any vehicles in the lane that you want to enter.
Also this:
- give way to all vehicles that will cross your path from your right as you enter the roundabout.
In your case since you were in a separate lane, the give way to the right probably doesn't apply.