Worried ... Plz guid me

Roshaan
According to my last menstrual date im 8 weeks today but today i had my first ultrasound n the doc said the baby is 5weeks and 5 days everything else is normal ... Its was the external utrine ultrasound .... Is it fine or there is sumthing to worries .... My follow up ultrasound is after 2 weeks to see tge progress .... 
Ps: im getting brown blood spots from alst 2 days on n off 
Wat to think wat to do i really dont knw