Second scan

Supposedly 8 weeks based on first day of last period. First scan in supposedly 7th week showed sac only. After one week, report dates sac size 1.34cm at 6week 2 days. More brown spotting these 2 days. Should I be worried? Still no yolk sac. Doc said normal, next scan in 2 weeks. 🙇🏻‍♀️