explain this to me please

I got my period October 28th, meaning I couldn’t have been pregnant in october. I ovulated the 11th of November, and then missed my period when it was supposed to come the 25th of November. which means I couldn’t actually be almost 6 weeks. it’s just going off the first day of my last period (october) does that mean when I go for the ultrasound they’re going to say that i’m not actually as far along as I think I am? or what? this is messing with me! this probably sounds so crazy but it’s my first child and no one has answer for me, i’m truly curious! I was in the hospital November 6-10 and they didn’t tell me I was pregnant and the reason I was there just concerns me for the baby in general!