Small for Gestational Age

"Small for gestational age means the unborn baby is smaller than expected for the number of weeks of pregnancy" . Hi there I'm at 21 weeks but my baby size is around 19 weeks only. Maybe most of it is my fault, as I don't drink any materna milk bcs I tend to gain weight very quickly and honestly my diet is not much of a healthy, balanced diet anyway. I'll try to change my eating habits from now own in hopes that I can help my baby to grow normally. However, I would just like to know if anyone here had/ is having the same experience. I need to know what are the possibilities that things will get better and the baby will be delivered in a healthy condition, and what are the possibilities that the baby is will face any complication during and after pregnancy? Tysm on your feedbacks ????