Yes, Plan B can delay your period, make you miss it, make it come early, and do other funky things to your cycle. The sooner you take it to the unprotected sex, the more likely it is to work. Since you took it within the 72 hour time slot, you are most likely fine and just experiencing a side effect. Keep in mind the app goes based off an average and can't predict exactly when you ovulate, which is why it's best never to go unprotected.
If it will ease your mind, you can ask your doctor for a blood test as they are more sensitive than a urine test.
I mean I took a EPT digital pregnancy test. The same test I took when I was 3 weeks pregnant with my daughter in 2012..