LMP at 7wks but ultrasound at 5wk2d??

I had a myomectomy done in Jan2024 for 1 fibroid, others still remaining, so my cycle is a bit off now moving from 30, 32 days. Had my first scan today but they had issues finding anything at all. Had blood test and showed by hcg levels at 5000. So had scan done with o&g and they found a tiny sac at 0.45cm and dated 5wk2d, but according to my lmp should be 7wks. I'm freaking out. is this because it's not growing as expected? Or is it coz my cycle is off? But that's such a big diff from 7wks to 5wks.