Due date keeps getting pushed back

Okay so my first ultrasound my dr told me my gestational sac was measuring 5 weeks 6 days i went to the er a day later due to bleeding and they told me my sac was measuring only 5 weeks 5 days fast forward to yesterday i should have been 7 weeks 5 days and the er told me the baby was measuring 6 weeks 6 days. The 7 weeks 5 days makes the most sense to me due to the timing of my dark bfp i would have only been 2 weeks pregnant when i got the super dark positive if i was only 6 weeks 6 days and it just doesnt seem right to me but who knows im not a dr. Is it possible for baby to measure a week behind this early? And i know for a fact i didnt ovulate later in my cycle.