I am brand new here, and in fact am still working through my pre-reqs. I've not even APPLIED to nursing school, so I could be totally, totally wrong about this. However, I found this link:
http://www.allnursingschools.com/faqs/nclex.php
...if you look under "Length of Test", it looks to me like you're fine. However, it doesn't specifically state that the test will "end itself" as soon as you've answered enough questions to show that you've passed, so I could be completely wrong.
I'd love it if others would weigh in on this...I've been curious about the NCLEX myself!
Don't beat yourself up!
Penny