I need help! Had my first <a href="https://glowing.com/glow-fertility-program">iui</a>... got pregnant first time.

I went to my appt last week was measuring 5w2d (1day behind what I should of been-5w3d) dr assured me it was fine and we saw the sack and a small yolk sack.

Today, i went to my appt I am only measuring 5w4d and am supposed to be 6w3d. But my sack and yolk are bigger and he spotted the fetal pole (no heartbeat)...

Is it probable that I am going to miscarry at this rate? My dates are on point (he said) due to me having an <a href="https://glowing.com/glow-fertility-program">iui</a>.