Baby measuring 6 days behind.

Recently I went for my first scan at 7 weeks 6 days but doctors says I'm about 7 weeks in when my apps says 7 weeks 6 days,is it normal to be measuring 6 days behind? Next ultrasound will be at my suppose 10 weeks 6 days.. (Sonographer didn't even let me hear my baby's heartbeat thou...she only shows me the flickering of it..)