First US tomorrow

Noelle
But I have a question. 
My LMP was Feb 24, so that would make me 6w6d tomorrow. 
But I know roughly when I ovulated, which was either March 13, 14, or 15. So wouldn't that make me less weeks? Like closer to only 4? I just want to be prepared if baby isn't as big tomorrow. I don't want to freak out and think I'm miscarrying when timing might just be off. The office is going by my LMP date, Im also worried they might not be able to find/see a heartbeat if I'm not as far along as I think I am 😥😥