Can I retest all questions without losing my previous data?
Yes! You are able to decide if you want to Test Incorrect items or Retest All items on a test.
If you do not see the choice when you click "Test", it is probably because it is the first time you are testing. Another reason could be that it is a test in a subject tab that is managed by your school or district, and they have selected whether they want you to Test Incorrect or Retest All for the tests in that Managed Subject Tab.
To see the student's answers from past test sessions, go to Details.