Doc made me an ultrasound appt because I'm 4cm too big. Should I be worried?

T&T=C

I went to my regular OB check up the other day and my doc and her intern kept remeasuring me. I asked what the problem was and they asked when I had my last ultrasound. I told them 18 weeks, I am now 34. My doctor and her intern leave the room then only to send intern boy wonder back in too tell me I'm measuring too big. To which I thought I know we are huge, then I asked,"How big?" The doc comes back and they both tell me, "4 cm too big" like I am asking for nuclear launch codes or something.

I thought it wasn't a big deal but now it's the night before and I am starting to worry. Should I be arranging for a sitter for my daughter and have hospital bags ready tonight?

I'm really freaked out. Thanks for your help.