The most common reasons for this is one of 3 things, 1st, channel mapping for your transmitter. Your transmitter neeeds to match the stick inputs in betaflight (roll moves with your right stick side to side movement, pitch moves with your right stick up and down movements etc), this is called rc channel mapping and if its not setup proerply it will cause this issue.
2nd reason is motor mapping, in order for your drone to fly, each motor has to fire up in a specific order and direction. Betaflight will show in a diagram on the configuration tab or the motor tab the layout of the motor order and the direction each one needs to rotate.
3rd and last reason is the orientation of the flgiht controller, some fc's have an arrow on the top indicating which way its default set to be installed in the drone. If you have it rotated or flipped then you need to change the boards orientation in betaflight in the configuration tab by changing the roll, pitch or yaw degrees to match the 3d model shown in the setup tab (if fc is flipped upside down then change roll to 180 degrees to correct it so the gyro knows how to process the data). If you still have issues please contact us directly as there may be a hardware or setup issue.