The main issue is likely parallax, not just lens distortion. If the camera was rotated by moving your body or the camera position instead of rotating around the lens’s no-parallax point, foreground and background elements shift relative to each other and won’t stitch cleanly.

Applying lens correction before stitching can sometimes make things worse if the stitcher was expecting the original geometry.

What you can try now:

• Use a more capable stitcher such as Hugin or PTGui.
• Manually add/control control points to improve alignment.
• Use masking to choose which parts of each frame appear in the final pano.

For future panos:

• Rotate the camera around the lens’s no-parallax point.
• A tripod with a panoramic head helps a lot.
• If you don’t have one, carefully pivot the camera as consistently as possible by hand.

In short: some cleanup may be possible in software, but if parallax is strong, no amount of warping will fully fix it.