Predicted miscarriage

My doc told me yesterday that I am going to have a miscarriage and I feel so emotional and stuck just waiting for it to happen. I bled lightly for the first 3 weeks of my pregnancy & had high HCG levels in my first blood test but they didn’t increase at all in the 2days following and only went up like 10% another 2 days later. I had a scan at 5 weeks which showed the gestational sac measuring 5w1d and then another at 6 weeks & the sac only measured 5w3d which is when the doc told me to expect the worst. My question is, when will this miscarriage happen?? Is there a chance it will take awhile? I just want to move forward & try again.