Pixhawk 4 mini fly test

hello today i did my first test fly it when crazy unstable and land down hard …few time i did the fly test and its the same …when it took off from the ground started to going crazy flying up down left right by it self …
The installation is with quadcopter x and gps is place beside the fc pixhawk 4 mini …is this ok or m i wrong for this installation ???
The calibration and the flight controller orientation of yaw= 270* is prefect no error and problem …remote controller radiomaster TX16S and receiver frsky RX8R pro Need some help here …tqvm