BFP but anxious about losing it

Sara
After a chemical miscarriage on 12/9 and no period or faint line on January 8-13th..... I finally got my BFP. Went to the OB to confirm they a quantative HCG blood test. Came back at 63... I was petrified... then Wednesday it came back at 129.... still scared.... and it supposed to double every 48 hours. Friday was 319! 
I'm not sure when I'm due. When I ovulated. My cycle was thrown off a bit due to the miscarriage. The number seems low but my doc doesn't seem concerned. One more blood test Wednesday of this week. Then ultrasound on 1/30. Could use some sticky baby dust
4th and final baby (I have 3 girls so far)