It really nice to know that your 700 grams baby is now 4.8 kgs without any health problem. Its not like that a low birth weight
baby will be smaller in childhood or adulthood.
Overall attainment of height depends on parental height, genetics,environmental factors and nutrition.
According to birth weight your baby's height and weight is adequate. A newborn with normal birth weight gains about three times weight till 14 month of age and your baby has gained about 7 times. This indicates that he will attain normal height and weight in next 1-2 years.
You are trying your best for maintaining proper nutrition which is the only factor which can be managed.
You are giving all the nutrient, just take care of proper calories (about 100 calories per kg per day).