You need to put all the slips you have for the year on your tax return. If you don’t include your T2202A, you won’t be able to use, transfer or carry-forward your tuition amounts. OSAP is a separate thing.
Regarding the drop in your refund, what is most likely happening is TurboTax is automatically claiming the Working Income Tax Benefit when you put in your employment amounts. The WITB is a refundable tax credit meant to provide tax relief for low-income individuals and families already in the workforce, and to encourage other Canadians to enter the workforce. However, students who went to school full-time for more than 13 weeks in the year are generally not eligible for this credit.
So if you tell TurboTax you had a low income, it will claim the WITB, and you refund will go up. But if you later add information that makes you ineligible for the WITB (ex: 4 months of school instead of 3), you no longer qualify, and the credit will be removed from his refund.
To make sure that TurboTax Online knows that you don’t wish to apply for this credit:
Click “Find” and search for “Working”, then select “Working Income Tax Benefit” from the list and click on the “Go” button.
Select “No” next to the question “Do you want to see if you qualify for the Working Income Tax Benefit?”. Click the “Continue” button to save.