I have had this happen.  I find that, when I go back to the video, I stopped it before the end and there are a few seconds left to watch.  You must watch all the way to the end for the video to be marked complete.

But I fully watched my videos---thats why I am asking 

If you watched the videos to the end and did not fast-forward, you may want to open a ticket with the Support Desk: https://khanacademy.zendesk.com/

Hi there,

Here's an article that may explain why the videos are not being marked as completed on your account: https://support.khanacademy.org/hc/en-us/articles/115002789111-Why-aren-t-videos-showing-as-completed-in-my-profile-

If the suggestions there do not help, please submit a support ticket as AD Baker suggested.

I hope this helps!