fundal height

I read that your fundal height should match your week. I'm 18 weeks pregnant (supposedly) and my fundal height is 27. I know this probably sounds stupid because my doctor would know more about this than me, but I think she calculated my due date wrong. I'm really nervous, should I say something about it or leave it alone? I know that they're wrong but I don't think my doctor will do anything and there isn't anymore around where I live.