Welcome to the forum !
What phantom do you have ?
What software are you running ?
If it's a P2 did you calibrate first in RC assistant then agin in phantom assistant ?
Have you flown at all or is it new ?
So make sure you are flipping the right switch up and down at least 5 times. Then you need to do a 360 with the phantom and flip it sideways, and do another 360. I have had in the past disturbances from the concrete and rebar affecting the calibration. Try moving it in the grass.