How much likely is my baby weight during labor when its 3.7 lbs already in 28 weeks with gestational diabetes please help! what weight should i expect?

Depends on you: The present weight is within normal range.The final weight will depend a lot on your ability to keep your blood sugar in a good range. Baby makes it's own insulin & will use/deposit whatever you send across. If your blood sugar levels are high, baby will be more likely to be big, if kept normal, less so. The need for a C-section can be driven by this and many other factors which you cannot control