Should I worry?

Went to the drs today to get my first ultrasound. I’ve been doing fertility treatments and my last period was June 3. I triggered (ovulated) on the 15th of June. My hCG numbers have been rising appropriately. I thought I was 5weeks 6days today. Today my hCG was 2,658 but my ultrasound only showed a gestational sac. And it measured at 4 weeks 5days. No yolk sac no fetal pole yet. The dr told me she is almost certain I will miscarry. So to prepare for one. Is there any hope? And success stories? Please reply. Thanks guys!