Good evening

This is my story ..im supposed to be 4weeks 3days today..started bleeding red but not that heavy..one pad was enough for the day..today is my second day bleeding and decided to go the doctor and he said its early for to do a scan ..the nurse checked my cervix using her finger and my womb had a tiny opening and she couldn't say for sure if it is a miscarriage or not ..i was then reffered to woman's clinic whereby they did a scan and saw no baby ..the doctor then concluded i miscarried.. I have no pains ..no clots ..im so confused . how accurate can a scan be at 4weeks