What Does Bleeding And Cramps With HCG Level 451 Suggest?

I went to the hospital yesterday. According to my last period I would be 7 weeks 2 days pregnant. I was spotting and once they did an ultrasound I started cramping and bleeding more. They did not see any baby in the ultrasound and my HCG level is 451. They told me if they don't go up I am going to miscarry. Is it possible that they can go up and I can continue my pregnancy?