Week day calcutations

Ok so Glow and most of my pregnancy apps have me at 15w6d. My due date is 8/19. My dr told me I'm 15w5d, not a big deal as she is basing her current status on one of the 3 original measurements of baby around 8weeks. Well I went to the radiology department in my clinic to schedule my anatomy scan aka 20wk scan and based on Glow I will be 20w2d, but radiology says 20wks exactly. Anyone else having conflicting weeks-days from your apps and doctors?