Boyle's Law predicts what will happen to a gas when the temperature is constant and the pressure/volume change.
If the balloon is originally at atmospheric pressure of, say, 101.325 kPa, then taking it to a pressure of 202 kPa (increase in pressure) with a constant temperature, will decrease the volume of the balloon and it will shrink in size.
P1V1 = P2V2
(101.325)(V1) = (202 kPa)(V2)
So V2 will be 101.325V1/202 = 0.5V2 or put another way, the volume of the balloon will be about 1/2 of what it was .