Yes, you do need to include your pension buyback contributions on your income tax return.
On-Line version: to enter them navigate to the RRSP Tab > RRSP Profile > continue to the Registered Pension Plan Deduction screen and enter the $value of your receipt in past services contribution for after 1989 entry field.
Desktop Easy Step version: navigate to the RRSP tab > RRSP Profile > chose the box "Claim for undeducted contributions... for past service" (bottom box). continue to the Registered Pension Plan Deduction screen and enter the $value of your receipt in past services contribution for after 1989 entry field.