Anak, please check with your OB right away about this, they need to see the baby's heart rate in context with the ultrasound findings, kaya hindi ako makakapag-comment dito. A few of us mums have had similar concerns during pregnancy, at lagi naming sinasabi sa isa't isa na ang best reassurance talaga ay mula sa doctor na nakikita actual timing at development ng baby. Don't worry too much, pero get it checked ASAP para sa peace of mind mo.