+1 all that raymo said
Using a short focal length scope you will notice the problem less than a longer focal length scope, as with the longer scope you're zooming in more. For example, if I DARV with my C8 onboard, error is usually pretty apparent at 15 seconds. With my Esprit, at about 1/4 of the focal length of the C8, not so much, and I have to push out the length of the tracking time some more.
If it looks great with DARV taking an image like you have and still seeing some elongation, check whether or not the elongation is the same (direction, length) all over the image.
Regarding the double star thing, that would be the wind...or the scope got knocked...