For a workout to meet the completion requirement, please ensure that you are both a) watching the video in its entirety from start to finish, and b) ensure that you are not skipping ahead too much during a workout, as this will prevent the workout from registering as completed.
If you are already performing both of the above, then it is likely that the completion requirement has been met and you've received credit for completing the workout - please simply refresh your page for the checkmark to appear!