Could my baby have problems after birth? ?

I went to have an ultrasound today and my baby measured at 34 weeks everywhere but her abdomen which measures 31 to 32 weeks, the doctor says that this is what they may call a "head trunk discrepancy" or "growth retardation" but not IUGR (intro uterine growth restriction).... He said it could be from me being underweight when I got pregnant and also the fact that I didn't get enough protein in my diet in my first month and a half Or so of pregnancy because I didn't realize was pregnant because I was still bleeding/spotting. I already love this child so much and I want to do everything possible to make sure she is healthy and born without any problems... Does anyone know if this is going to cause my baby problems afterbirth and what I should do to help her little abdomen catch up with the rest of her body? She weighs four pounds and I am 33.5 weeks pregnant is that a normal weight for this time as well? I'm just afraid and want to do everything possible for my little girl to be healthy.