Hi @Mary,
Could you please clarify what plagiarism checking tool your school is licensed to use?
Unicheck is one of the software used by higher educational institutions all over the world. It is easily integrated into Canvas.
Unicheck has special functionality for students to pre-check their drafts before the final submission. Your instructor has to enable this option in an assignment and set the number of pre-check attempts.

For example, as you can see in the picture below, an instructor provided students with 3 pre-check attempts.
The more detailed instructions and guidelines on how to check drafts and submit a final paper, you may check following THE LINK.
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