Hi,
I got my regular periods on 1st of Jan 2013 for five days. I got recently married on Jan 17th 2013. I found blood spotings from 27th Jan which went on for a week I thought. So I decided to go for a pregnancy check on feb 8th 2013 and its +ve. The scan impression shows gestation sac corresponding to 6 weeks. I am confused as my marital status is only for 3 weeks till Feb 8th. Can some one explain how is it?

If you didn't have sex before marriage, the person interpreting the scan made a mistake. They usually don't get women who get pregnant the first time they have sex, and they calculate based on last period. The embryo is still VERY tiny and it was easy to interpret the scan carelessly (or not going by the scan at all). You could have waited quite a while for a first scan.
(And it's common to spot the first month of pregnancy or even have a light period.)

You had sex before you were married ?

Or as normal, there is no exact method of getting an exact conception date, all conceptions dates are estimates at best