2 other things to check:
1) Is the bit the correct width? If it is too narrow it can pinch, and if too wide it can slide around too much.
2) Is the bit the ideal diameter for your horse? Thinner bits are more severe than thicker bits. To better understand this concept, get a friend to help you and have the friend lay a piece of string across your bare are, grap the two ends and pull down. The do the same thing with a wide piece of ribbon. The narrower piece of string will put all the force onto a smaller area of your arm, while the wider ribbon will spread the same amount of force over a wider area, so the amount of force per square inch will be less. Think of stillto heels versus thicker cuban heels. Stiletto heels have been known to literally put dents into wooden