If the drone isn't at the center of the fence, you get perspective distortion (the side of the fence farther from the drone is smaller, so a rectangle looks like a trapeze. This is fixable with the Perspective tool in "Corrective" mode.
If the fence looks like an ellipse, the drone must have some kind if fish-eye lens. You can try to compensate this with Filters > Distorts > Lens distortion.
If the fence looks like an ellipse, the drone must have some kind if fish-eye lens. You can try to compensate this with Filters > Distorts > Lens distortion.