Warped forend ,

[Tom]

Hi
I made a new forend (wood) for my lifter gun. It took a ridiculas amount of time but I was shooting for perfection. The inlet job on the barrels was spot on. Finished it up put it on the rack and was pleased with the result. Shot skeet with it yesterday and noticed the front from the key forward has lifted almost 1/8 of an inch ! And it has a slight twist, a little higher on one side than the other.
The wood is well seasoned very figured wood. I cut it out of the same wood I made the stock out of. I don't know what happened but I'm guessing when I cut the slot for the keyway in possibly I relived some kind of internal stress and it warped. Or possibly the whole thing would have warped if it wasn't for the key and the iron holding the rear in place.

Frustration and disappointment would be an understatement for me at this point.
I put a clamp on the tip securing it to the barrel , but I'm sure when I release the clamp it will just spring back to where it was.
Any ideas how to fix this ?
And more importantly , how can I prevent this from ever happening again ?
I'm not giving up but won't do anymore woodworking until I understand this, I have a tremendous amount of time invested in this.
The wood sat in a friend's basement for years with both ends sealed. The stock from the same block of wood has no issues.
Thanks for any suggestions, Tom