Tell someone or document it before you close it up.
I installed the duct or fitting and now it does not line up. What do I check?
Do not force the joint. Check elevation, rotation, centerline, wrong fitting, missing offset, hanger height, gasket/flange clearance, and whether another trade or revised drawing changed the path.
Check elevation, rotation, tag, revision, support height, and conflicts before forcing the joint.
Do not suck a bad fit together with screws, one flange bolt, strap tension, or mastic. Do not bury a twisted joint.
Check
Correct fitting/tag
Correct drawing revision
BOD/TOD and centerline
Hanger height and side pressure
Nearby trade conflicts
Steps
Support the duct so the joint is not carrying weight.
Check BOD/TOD, centerline, rotation, and fitting orientation.
Compare the piece tag and latest drawing/revision.
Check hangers/rods for height or side pull.
Ask whether to adjust hangers, reorder, add offset, or hold for coordination.
Say this to your foreman
This duct/fitting is installed but will not line up at [joint/location]. I checked tag/revision/elevation. Do you want me to adjust hangers, hold the run, or ask for a coordination fix?