Getting started

Have you been transferring info from previous years returns or using CRA Auto Fill? Because that's the only way the limit information would populate without you entering it. 

If you transfer info from year to year, that could spread a mistake if you don't manually enter the correct limit. 

The deduction is partially based off the limit, so if the limit is wrong, then that could cause you to claim too large (or too small) a deduction.