Do not claim an amount as "Payments related to your Principal Residence" for rent paid for your student residence.

You can only claim rent you paid "somewhere else" as per CRA rules.

"If you lived in a designated Ontario university, college, or private school residence, place a tick beside box 6114 on Form ON-Ben . You will get $25 for the property tax component of the OEPTC for the part of the year that you lived in that residence. If you also lived somewhere else in Ontario for part of the year and rent and/or property tax was paid by or for you, enter the amount paid beside box 6110 and/or box 6112 on Form ON-BEN, as applicable. To find out if your residence is designated, go to ontario.ca/finance"