8 week ultrasound- twins! One is a week behind.

Emely
Baby A measured 8 weeks but Baby B was at 7 weeks, 1 day. Baby A's heart rate was 156 and Baby B's was 145. My doctor put me on high risk and wants me to come back on the 25th for another ultrasound to check that he's growing. Has anyone ever experienced this? Is there anything I can do?