What Does This Ultrasound Test Result For Pregnancy Indicate?

Hi I have had some brown spotting since week 5 of my pregnancy. In week six they did a vaginal US and found a sac but no fetus. My HCG levels were at 28,000. Two days later they have found they embryo but say there is no heartbeat and my HCG level has only risen slightly to 31,000. they have prescribed me some tablets to induce an abortion. My question is, is it likely or possible if I wait another week until I m in my 8th week that there maybe a heart beat and the sac size will develop further or am I clutching at straws?