Does A Smaller Embryo Than What It Has To Be Mean I'm Going To Have A Miscarriage ?

i am 33 of age, i had my last menstral period on the 9 of feb2011, and on the 13 of march i got a positive pregnancy test, and on 17 of march my hcg was 1224,0 and on 21 of march ,just some few days letter, it was 5152,0, and on 31 of march i went to my doc for ultrasound , and he saw just a gestation sag measured 17 to 20mm and a littel white mark in the middel measured 2 mm, and the doctor told me the ultrasound is showing my pregnancy as 5weeks of which by his calculation i should be 7weeks gone, so maybe i am going to get a misscarage, or maybe the embroy is still smaller that can not be seen now, but he was hopeing to see the embroy and a heartbeat on that day ,so mynext apointment is on 14 of april , i cann,t sleep, bc i which to see my baby this time ,after two misscarages, pls any help of good answer will heal me. waiting.