First Ultrasound. First pregnancy. Please help!

Roxy
Hello ladies,
I went last Thursday for my first appointment. I was supposed to be almost 6 weeks but they told me that it seems that I'm almost 5. The doctor told me to come back on Tuesday, because they couldn't measure the baby to give me an estimate of how far along I am. and also mentioned that she will do more blood work. Is this normal? I'm so scared. 
Thanks for your help!