Dr said everything looked great. She said my placebo was kinda low but she said it all depends on…

Dr said everything looked great. She said my placebo was kinda low but she said it all depends on where the baby first implants. Should I be worried? Also I had a ultra sound at 7 weeks and today at 20 weeks and they scheduled another one in 4 weeks I don't remember having this many. Is there something there not telling me