Wtf/ kinda of long

I tell the genius RN that I have always had a 35 day cycle. She says to determined your due date we have to go by your last cycle. Yes, I know that but isn't that using a 28 day cycle theory. Freaking genius said she has never heard of such a thing. Wth! They want to schedule me for my six week US ( hx of mmc) next week. Excuse me, I won't be six weeks. You are a week ahead mam. I ovulate day 21 and I had sex in day 20 and 21 only, Why I'm stressed because the US will not show where they would like me to be and I will be stressed. Pissed and don't what to do!