Slow rising hcg ... please read!

So my beta numbers were doubling and I had one done 3/3 which was 161 and today on 3/8 (taken a half hour earlier) was 499 (57.3% increase in 48 hours and doubling every 73.5 days). I was driving to the airport to go on a family vacation to Florida and the doctor called me frantic and said I needed to go to the hospital to have an ultrasound done right away to see if I’m having an ectopic. They saw a small sac in my uterus so no signs of ectopic so far. They said I still could miscarry and “it doesn’t look good”. But I have to go back Sunday for another beta. Has anyone had experience similar to this? And had a successful pregnancy? I’m so nervous that I will miscarry :(

Update** I had to have a D&C today because the hcg stopped rising and they couldn’t see a yolk sac and I am devastated 😢 onto IUI number 3....