Good day!
How can I cancel a process: by interrupting and drawing a separate diagram, inside the main process, or are there other ways?
Hey Maria & welcome to the forum! 
What you have modeled looks pretty good so far.
In order to interrupt a process from a “business point of view”, you would typically make use of an event based subprocess as you did.
It is also a good practice to model it this way. So I wouldn’t encourage you to do it differently.
Maybe this Best Practice Guide can help you in as well:
https://camunda.com/best-practices/modeling-beyond-the-happy-path/#_dealing_with_strong_canceling_the_process_strong
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Thank you!