What does self-matching mean?
Answer
Self-matching can occur when a student has submitted an assignment to a class and then later submits the same assignment to another class. When this happens the student will get a similarity score of 100 as the new submission is a perfect match with their previous one.
You can find information on how and why this happens in this Turnitin article.
To confirm that your high score is a result of self matching you can check the sources you matched with by following this FAQ.