15cm at 16 weeks?!

Rhianna

I went for my gender scan yesterday and it did include a 4D picture of the baby. On the measurements up on top of the photo it was 15cm. I’ve been reading up on sizes and he should be 11.6cm. I’m just wondering if anybody has had the same issue as me? Are they measuring head to toe or crown to rump I have no idea. First pregnancy