Firstly, don't stress too much, as if your baby is growing fast it does mean a more difficult birth (I had a 9.5 pounder), but bubs will still be healthy.

Basically, if you have high blood sugar levels then there is a lot of sugar available which makes babies grow fatter than average. To avoid this you want to follow a diabetic style diet to manage your blood sugar levels. It's not just sugary foods that can make your blood sugar levels stay high, but also carbs such as bread, potatoes, pasta, etc. Generally eating lots of vegetables (inc raw such as lettuce/carrot) as well as good serves of protein (meat/nuts/chickpeas/etc) and keeping your carb intake to lower portions should help manage things.

If you look up paleo-primal diet you can find lots of recipies etc that meet these requirements, and hopefully find food that you like!

I have a blood glucose meter (I'm pre-diabetic) that I use to check what foods spike my blood sugar levels. You can get without prescriptions (though costs more) if you want to go the extra mile and get one to check what your blood sugars are doing.