Hi. Its 9 Days Passed Since My Periods Are Missed.

Hi. Its 9 days passed since my periods are missed. On a pregnancy strip it is coming positive but in blood test my hcg is coming 120 on 7th day. My doctor said that it should be 2000 at this time. I m really worried. I dont want miscarriage. Kindly suggest me what to do. How to make it a healthy pregnancy? Please reply me as soon as possible.