6w6d with 2 sacs and no heartbeat

Hi...this was my first ultrasound this pregnancy and we seen 2 sacs...well in one sac we really had to find the baby forming but she spotted it but the second we seen nothing and she said the shape was abnormal...I thought it was weird at 6 weeks not to hear a heartbeat and a weird shape sac IS IT TWINS??? so I'm worried I go back on Tuesday to see if anything change...has anyone had this happen before