Due date confusion

The first day of my last period was nov 25. 14 well dec 26 I got 3positive tests and today I got my proof if pregnancy from my local  health dept. well according to Glow I am 4weeks 6 days and due sept 5th 2015 but the lady at the health dept told me that I am due oct 4th 2015..that isn't possible is it?? I mean that's 10 months into the new year not counting the beginning of my last cycle..I have a dr appt but can't get in until February 4th..should I go by glows due date?? Was it accurate for all of you?