5 week ultrasound

Went to the clinic today. I measured 5wk 1 day via transvaginal ultrasound. According to periods I should be around 7 weeks. It took them so long to find the gestational sak. They sent me for a HCG which I hadn’t had done yet. I have irregular periods and PCOS. just curious if this has happened to anyone. I’ll get my HCG results back in the morning. Should I be worried.