If you want your crossbow bolt to fly straight, there are a few things you need to do. Make sure the crossbow is calibrated properly first. You should also use good quality bolts that fit snugly on your crossbow and are well-made. When you shoot the crossbow, keep it steady and aim carefully. You should also practice regularly to fine-tune your aim and learn how the crossbow works. With time and effort, you should be able to get your bolts flying fairly straight consistently.