Period might be late?

So I’ve only been using the eve app for 3 months. The first month my period was from the 20th-26th. The second month, last month, it was from the 13th-17th. It hasn’t came this month. It is now the 19th. Before I got the eve app my periods were always around the 20th of each month except last month. So now the eve app says i’m 8 days late because it expected me to start earlier since i did last month. Is this accurate? Should I be concerned i’m pregnant or should I wait since it’s just now going to be the 20th tomorrow. I have been sexually active with no condoms/birth control but using the P/O method. Please give your opinions I’m freaking out I have never wanted my period to come so bad.