Dating with this app? Confused!

Hello! Today I had my early scan as I have had two previous miscarriages. According to Glow I should have been 6 weeks 3 days but the scan had dated me 5 weeks exactly. We did see a heart beat fluttering away but I am worried too as I started spotting this morning and with the dates I'm so confused. Do the hospital date it from the date of conception not missed period? Any help would be much appreciated! Here is my little bean!!