If a user does not wish to leave a rating for an activity, they can click on Cancel when the rating window is presented. 
The user can rate the activity when they have thought about their response or have more time to do so.
Navigate to the My Activities area.
Click on the Completed link in the top right-hand corner.
Click on the Rate the Activity link beneath the activity.
Click on the number of stars which represent the experience of the activity. Add a comment (this may or may not be a mandatory field).
Click on Submit.