Oh my goodness, I really feel for you right now because getting that kind of news at 20 weeks must feel so overwhelming and scary. When I was pregnant with my second, I had some growth concerns flagged around a similar time and I remember just crying the whole drive home from the hospital. What helped me most was staying closely in touch with my gynae, going for all the monitoring appointments without skipping a single one, and just resting as much as I could so my body could focus on the baby.