Cried at dinner because a family friend said my baby’s head is flat

Don’t know what flair to use but mostly just want to vent. I have a 4 month old and she’s perfect. We went to dinner tonight and I go to take her out of her car seat and our family friend immediately goes “you need to not let her spend so much time on her back, her head is getting flat.” We do tummy time, and she’s not rolling yet so yeah she spends a good amount of time on her back, but honestly her head isn’t even flat. I don’t know if I’m just sensitive but I already have an overwhelming sense of guilt daily that I’m not doing enough and that just sent me over. I immediately give her to her dad and go to the bathroom and cry about it. I’m not a good liar so everyone knew I was crying when I came back and the rest of dinner was just awkward and me saying I cried because I’m anxious. Ugh I wish people just wouldn’t say anything :(