Am I still be pregnant? I'm terribly scared ?

Im 4 weeks pregnant. This is may 2nd pregnancy and I have no history of miscarriage. This is my 1st ultrasound since I have brown spotting for 12 days. Can anyone please enlighten me that this can be a false interpretation? The OB told me that retained product conception means that I have an incomplete miscarriage, or ectopic. Is that true? Or is it early to say? I have read that there were cases na may false interpretation minsan kapag nagpa ultrasound ka at 4weeks palang. Pero bakit ganun ung impression sakin? Makapal daw lining ko and hindi naman heavy bleeding ko. As in brown spotting lang yung parang patapos na mens mo. ? I feel so down ?