When did I conceive?

Hoping someone can help!  I'm pregnant and my LMP was 1st February and as my other half works away there's only 2 days in February when I could have fallen pregnant. 

The two dates are 14th Feb and 27th feb.... So how far along would I be?

The reason I'm asking is because on 27th March I had a private scan, in the hope that we'd see baby and can break the news to our parents as I worked out I should have been 7wks 6days then.... However on the scan there was no baby just an empty sac.  Since then my pregnancy symptoms have completely vanished and I'm going out of my mind worrying something is wrong.  The lady at the scan suggested I come back in 10-14days and the wait is agony!  

Maybe I'm not as far on as I thought?!  

Any advice would be lovely x