Plan B during fertile days

Had unprotected sex on February 26 which according to this app was a fertile day. I took plan b a few hours later. What do you think is the likely hood plan b did not work. My ovulation has been all over the place before. Usually I ovulate later rather than earlier, however, it always changes. I took plan b more out of fear of actually being pregnant because I was doubting my ability. I had a really horrible miscarriage in July and have a lot of fear associated with pregnancy now. However we continued having unprotected sex after because we aren’t necessarily trying but not preventing. So if it happens it happens.