Blighted ovum at 4 weeks?

I found out really early I was 4 weeks pregnant, I started bleeding 3 days ago with bad cramping pain on day 2. Pain and bleeding have since subsided. Only light bleeding. Dark brown and red in colour.

I went for an ultrasound today both internal and external and I was told that I had a gestational sac but nothing inside. I was told it could possibly be a blighted ovum and to come back in 2 or so weeks when I’m around 6-7 weeks.

This will be the hardest time to wait but does anyone have any insight or advice? Is it even possible to say for sure it’s an invalid pregnancy when im only 4weeks and it’s hard to see anything at this time?

My HCG levels were 16 (3weeks4days)

And 67(4weeks2days)

I will return for another blood test in a days time.