1. Right click on 'Catalog Task Activity' and select 'Add Condition.
2. Add the Condition as in the attached pic
3. Double click on 'Always' condition and modify as shown, Make sure to remove condition (true)
4. You now have 2 Conditions for when this task completes
5. Draw the line from 'Cancel' to a Workflow Activity Set Value where you indicate the Stage as Request Cancelled

When the sc_task is closed as cancelled (state = 10, activity.result = 10), it will take the line desired in your workflow to 'Cancel' the RITM, then the REQ if only one RITM.