First of all- their weight guesses are just that; guesses. They can be off by a pound or two either way. Also, babies all grow at different rates. Some babies are born large, others small, others average.
If your doctor is concerned about you having another big baby, then maybe you can request an induction at 38-39 weeks.
can't say whether you'll have a big baby or not, as we don't know when he's gonna decide to join the world and his weight won't truly be known till he's weighed. you can always opt for a cesarian if it's really freaking you out. best of luck.