Hi
The 17 notes C scale in the scale finder is just the C scale (8 notes) being played twice in two different octaves.

You probably are already doing those videos but I suggest you take a look at the guitar fundementals videos in the core learning system. All that stuff is very well explained there. If you already are looking at them, in a couple of videos you would have found the answer of your question today :)

Have fun with your learning.