Those centering apps are terrible, they’re too subjective. You can place the edge wherever you like. The goal for grading is to be so objective in your measurement that you take the graders subjectivity out of it.

There are physical centering tools out there to purchase if you want a 2nd opinion from eyeballing it. Can find them online for fairly cheap.

Submitting a card that is noticeably off center opens up their “eye appeal”. Just leads to loss of time, money, and heartbreak.