I am a student that uses Canvas with Respondus LockDown browser for remote exam taking. I and several students in my class have accidentally submitted exams before we have properly finished. For example, clicking "Submit exam" instead of "Next question." Note: the “submit exam” button and “Next question” buttons are the same spot and it has caused accidental submissions; If you happen to be not paying attention, it's very easy to submit your exam before you can go back and review your flagged questions.
I suggest Canvas makes a pop up window that asks “Are you sure you want to submit your exam?” before submitting and closing the exam window.