Have you had ordinary periods since the miscarriage?
If you did retain tissue from the miscarriage, it is likely that you would have continued to have an hCG reading and that your periods would have unusual, or odd, or you would have had constant light bleeding. Did any of that happen?
Did the doctor run hCG tests after the miscarriage to confirm that no tissue had been left behind?
You could see your ob/gyn and explain what recently happened, and see if he or she wants to do either an ultrasound or an MRI of your uterus, just to be sure the uterus is clear with a normal endometrium.