Hello from JustAnswer.
The norethindrone is a progestin, a medicine that is similar to the natural progesterone.
By taking progesterone for 10 days, this would reset your cycles, but also may mess up your cycles for a month or two. Although the cycling may re-establish with ongoing periods on the 8th, if you are one of the women in whom it can mess up the cycles for a month or two, it is impossible to predict what day of the month will be your period once the cycling stabilizes again.
It will not have any long-term adverse impact on your ovulation or fertility, per se, only the specific day of ovulation and fertility. However, until the cycling stabilizes again, it is impossible to predict when the day of ovulation will occur.
The app on your phone will also not be helpful until the cycling stabilizes. As I said, it will typically stabilize after a month or two, and then the app will be accurate again.
If I can provide any additional information, please let me know.