Dating scan dissapointment

I went to my first scan today, and calculating by my last period on 15th January I should be nearly 12 weeks. I missed my February period and done a pregnancy test on the 23rd feb and it was positive..

However I went today and they told me I’m only 4 weeks along and it’s too early to detect a heartbeat. I have to go back next week to see if the baby has progressed at all.

Has anyone else had this happen to them? This is gonna be a looooong week 😢