Just wondering....

Holly • 22 years old from Alabama. I have been married to my wonderful husband since Sept. 2012. We have a daughter. Our family was completed when our Son was born in November 2015.
Ok, so when I've been putting in the first day of my last period, I've been putting February 9. Going back and looking at my calender, I spotted on the 7th and 8th. I'm wondering, if the first day of my last period was the 7th or the 9th... just something that happened to cross my mind... have I been giving the wrong info?