If you have reached the end of the activity and can see the summary window it does not necessarily mean the activity is fully completed:
Please go back into the activity and make sure you have completed all tasks.
If there are videos in the activity, please make sure you have watched these until the playback has fully ended.
Complete the tasks, making sure to interact with all features, and you should then see a tick next to the activity.
This video demonstrates how to complete activities: