I just called my OB's office and spoke to the receptionist. I explained my situation and she ended up putting me through to OB himself! He's very nice though.

He explained that it's a carefully calculated date and that they try to see you at the very end of the necessary timeframe as possible. He said the bigger the baby the better the results and they try to get the baby as close to 85mm as possible (I think this was the measurement).

So all is good!

I feel a bit silly now! So my scan is still set for 2 weeks.