Possible missed abortion

Hello ladies, I had a quick question. Tuesday I had my drs appointment and due to previous miscarriages I had an ultrasound done ASAP. According to my last period I should be 7 weeks. When they did the ultrasound they saw a sac but no fetus. Immediately they send me to the hospital to get a vaginal ultrasound. Right there my sac measure 5 weeks. My hcg level went up from 670 to 17000 in two weeks. Should I be concerned? I have a next appointment on Tuesday to redo an ultrasound