HCG level

My HCG level was 203 the first time I tested. The 2nd time was 2 days later at 283. 4 days later, it was only 483. My HCG level did not double at a start. Can HCG double after that? I went for a trans varginal scan. There is a pregnancy sac. Yolk sac not visible at 5 weeks 5 days. Quite worried about it. Gynae says now it is up to the baby. Anything I can do to up my baby's chance?