Last Period VS Dating Scan

Hi mommy.. Last tuesday, i went to KK to scan my baby for 10weeks 3days?.. But I'm curious because at the screen of scanner show that my baby 9weeks 3days, means that it late for 6days.. Is it ok? And how about my due date, is it late 6days also? I need to refer based on my period cycle or the screen of scanner? Help me mommy...?