Question about 20 w scan

I had mine today and found out ibhave a pretty big placental lake.. big pocket of maternal blood.. or at least thats what they think it is. Also.. my baby girls abdomen is in the 40th percentile which is good measuring at 19w6d but her head, arms, and femurs are measuring 2 weeks behind at a 4 percentile! My dr seemed conserned but didnt want to scare me with a bunch of what ifs, she saod she wasnt sure what could be going on so I am scheduled tomorrow morning for a repeat sono at a high risk drs office.

Has anyone else been through this? Im just worried my baby won't be healthy.