hi chris,
In addition to Raymos points i'll add the following; I have trouble stacking photos taken with just a lens, you can turn the star detection threshold down to 5% and it will help with stacking.
from your picture it looks a bit out of focus so the program may be struggling with that also.
use live view then zoom in on a bright star that will help. I find that 8 seconds is about the sweet spot for that lens. here is what you can expect (same lens and camera)
https://www.flickr.com/photos/803366...n/photostream/
i'll note that no processing or stacking was done with those - how it is straight out of the camera.