Conception Dates?

So i am not exactly sure when i conceived but i know i had a cycle Feb 3 for 7 days and off of that they say my due date is Nov 9 but i want to be sure so i can know when to fly back to my hometown with the father. My assumed conception is Feb 17 and on March 14 i had a transvaginal ultrasound and I heard the heartbeat so i must have been 6 weeks around that time. I got taken off of my dads insurance shortly after so i could not get a dating scan i just want to be sure and when i finally was approved for my current insurance it

Was too late for them to get accurate measurements.