Weeks/Drs/Contracting

Estrella
Okay so maybe someone can help me understand what's going on lol. I went into the hospital on the 30th of December because I started contracting... everything was fine and I was sent home. I went back on the 1st of January due to contracting again... well needless to say the kept me over night due to the vaginal ultrasound I got... when I went in on the 30th my cervix length was at a 4. When I went back on 1st it was at a 2.7. So of course they did everything to try, and I say try because nothing is stopping these contractions... and they're not the Braxton Hix. But anyway... Dr said I'm 31 weeks and 5 days... and my due date is February 24th. But when I look on the app and it says 32 weeks and 4 days... how do these weeks work?. I'm also starting to think I'm just further along and my lil one is ready to come out. But because she's so small, Dr's can't tell lol