Concerned, early scan

I went for an early scan on Christmas <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> I was about 5w2 Days, the dr could only see the gestational sac no embryo or yolk sac.. see loads of women on here who are able to atleast see a yolk sac at an early scan. Trying not to be concerned. Is this normal or should I worry??