There are some cased where this scenario is possible:
The federal tuition amount should bring your federal tax payable to zero, not your final taxes which has two parts federal and provincial.
The tuition amount has been eliminated in many provinces since 2017.
I am not sure which province you are filing from.
You might want to check Line 42000 The Net Federal Tax > at least this amount should be zero
The provincial amount on Line 42800 might not be zero because your province doesn't have a tuition amount credit.
Tax deducted at source is reported on Lie 43700 > so if Line 42800 is higher you will end up owing taxes
I hope this was helpful