What was the exact error message that you got when could not file your return?
When you file your Quebec return by mail, you don't need to send anything except for the return. Keep your slips and other documentation for your records.
This CRA link tells you what is needed when you file your Federal return by mail: https://www.canada.ca/en/revenue-agency/services/tax/individuals/segments/students/what-you-include-...
