Well........no need to panic as you are NOT diabetic and only have a predisposition to it.
You don't drink, you don't smoke but we don't know how your blood pressure is.
You main problem is eating too much.............try to cut down on the amount you eat, I know it isn't easy, but that may well stave off the onset of Type 2 diabetes.
If you can't...then you can't.....just keep your fingers crossed and repeat your blood tests every 6 months.
Yes, swimming is good for you if you have access to a pool, but it isn't likely to be as effective as reducing your food intake.