I breastfeed but my baby isn’t “fat”

I see all these babies of girls I know who breastfeed and their baby has rolls on their arms and are so cute and chubby. . My girl is almost 8 weeks and I breastfeed her and formula feed her . Half time she bf and half time formula everyday. She she’s not “fat” . Am I doing something wrong ? Or are all babies just different ?? 😒 I’m sick of hearing that oh you bf your baby is so little and tiny.. 😒