5weeks and 3 days ultra sound

Bonita

As the calculations of my pregnancy I am supposed to be in my 6 weeks pregnant but when I went for the ultrasound they said I am 5 weeks and 3 days. Has this happend to any one else? I saw the little baby and the heartbeat was 103bmp is that normal? This is my second pregnancy. I lost my first one at round about 6 weeks. Can someone please help me with some answers?