Wrong due date?

According to my lmp I should be 11weeks 6days but at my ob appointment on ultrasound at my 8 weeks appointment their measurements put me at 10. Not much of a difference but isn't early to feel movement? This is my second child. I would think I'm just imagining it but I can use a Doppler app ( which says it doesn't work in early pregnancy) and immediately find a heart beat where I've felt the movement. I already am getting a baby bump and round ligament pain! I'm not sure if I'm further along or just wanting to tell myself I am. Lol. Anyone else have this experience?