I just received a Notice of Reassessment and I am confused as too what I did wrong

There may have been a change or amount that was caught when the CRA assessed your tax return. Please have a look at the article listed below from TurboTax to explain it further.

• Defining Notice of Assessment, Notice of Reassessment, Request for Information and Audit - https://turbotax.intuit.ca/tips/defining-notice-assessment-notice-reassessment-request-information-audit-8223