It is not uncommon for there to be a slight difference between the gestational age calculated based on the Last Menstrual Period (LMP) and the actual gestational age determined by ultrasound. This can happen due to variations in ovulation and fertilization. As for the fetal weight of approximately 2455 grams, it falls within a normal range for a pregnancy at this stage. However, it is important to remember that every pregnancy is unique, and individual factors such as maternal health and genetics can influence fetal growth. It would be best to discuss any concerns or questions with your healthcare provider who can provide personalized guidance based on your specific situation.