I'm so confused

I had my first ultrasound yesterday according to the Dr she put me at 13wks but the glow app has me at 9wks when the ultrasound tech checked the baby is measuring at 6wks and no heartbeat...now they are telling me that I will probably miscarry...I told the Dr I wanted to wait and have another ultrasound next week because maybe we are all wrong with the dates and after 7wks there should definitely be a heart beat...right? i havent had any pains, cramps or spotting. my heart is so saddened...this baby wasn't planned but always welcomed as all babies are blessings please keep us in your prayers I don't know what to think, feel, or believe...