Can someone explain this to me

So my ultrasound is measuring 5 weeks 4 days but my HCG level is VERY high. It started out in the mid 7,000’s at that point I was 5 weeks 1 day. Then I went back two days later and the baby was a day ahead from the last ultrasound so at that point it measured 5 weeks 4 days and my HCG is now in the mid 12,000’s. Can someone please explain to me why my HCG levels are so high and why the baby isn’t measuring to that.

First ultrasound

This isn’t mine but that’s what the second one looked like.