I believe you are correct, Anita.
This shows it well. You can see that a z score of 1.64 falls just inside the top of the 8th stanine, and below this it shows that this represents a score lower than 4 + a little bit %, so I would think you are correct, just going from this graph. (statistics are not my strong point)
Hiphip, please be mindful that people from any country, culture, or studying any syllabus can come here, You'll find that the probability of someone studying the same syllabus as you will have a low z score! :)