It’s been over 20 years since performing a column ignition switch R & R on an old Mopar…
First; move steering wheel left & right while trying to rotate cylinder. Sometimes the steering wheel lock mechanism binds causing cylinder to not fully rotate to “Off” for whatever reason, bent rod, binding linkage, loose stuff in the wrong place…
If I remember correctly, to remove that switch one has to depress a small button and turn the key. Sometimes that release button won’t fully pop back out after lock cylinder is installed because it is not fully push into position, or it is slightly clocked out of alignment, or the receiving hole was buggered during removal, and button won’t full extend.
If above did not help, remove the new switch run it through its full movement just to be sure it is working correctly, than operate the ignition switch box located lower on steering column via a rod with a large screwdriver inserted into spot where key cylinder engages switch linkage to see if it has full travel. That would be: Acc.; Off; On; and Start. If it won’t move through all positions, than something in that switch is hanging up, or during disassembly something got loose and is causing binding in the column.
Be genital, don’t force anything, doing so will just make more of a me$$.