New pressure treated wood has a tendency to curl and twist, cutting into it did not help when trying to make the lap joints.
You may get lucky if you did it the right way and used screws by taking it apart and see if the 2 X curled and just replace it with a good one.
Post a picture of the door so we can see if there's a better way to build it.
Not sure how you did it but I've been building the cross bucks on the back side using reguler 2 X's, That way there not going to curl, be exposted to the weather, not rot the siding and the cross buck because water lays on them.
I use Wood glue and ceramic coated decking screws.
if you tweak the door ( put pressure on it with your two feet and bend the door in or out with your hands at the top it will tell you which way it is warped). It might work best to build a new one or put a 2x4 on the door that is not flat but turned with the 1 1/2" against the door and the 3 1/2" sticking off the door and put screws in it through the plywood.This could help straighten the warp some. Worst case scenario is to adjust the stop to fit the newly warped door...