Question!!!

So I spoke with my OB bc my husband and I hsve been struggling to conceive. She said we should be trying on day 12, 14, 16, 18 and 20 from the day I start my period. If that is the case, it would mean this app has been telling me a week early that I am ovulating and we could be trying at the wrong time. Has anyone else experienced this and is there a way to change how the app estimates fertile dates? I will say it is always accurate when it comes to the day I start my period.