Your bike will turn when you tilt your device. Make sure to tilt it only when you want to make it turn.
If you feel that the bike is turning when it should not, please try placing your device screen up on a flat, horizontal surface without holding it in your hands. Without lifting the device, start a Single Player race and tap the right-hand half of the screen to accelerate until the bike reaches a point where it is completely in the air and not touching the ground.
At this point, the bike should not rotate left or right. Its angle should remain the same as it was when the bike lost contact with the track. In these conditions, if it turns left or right in the air, please contact our Customer Support team.