5 weeks and can spot heartbeat?

Went for my KKH appt yesterday. Based on LMP I’m coming 8 weeks but KKH say I’m at 5 weeks. Able to see heartbeat during the ultrasound too. Spotted another baby(?) below the one with heartbeat but doc say there’s no heartbeat yet and can only confirm if it’s twin pregnancy or a shadow/light reflection. Feeling really puzzled…..