Step 17: Troubleshooting ideas
--You can move it forward and backwards to figure out the area which produces the loudest tone.
Plugging the end
--Some whistles end up being loudest when you plug the other end with your finger, some when you don't plug the end.
--Sometimes it helps to hold the mouthpiece tightly while you blow your whistle. If that's the case, when you are satisfied with your configuration you can consider gluing the mouthpiece into place.
Try the above in several different configurations to find the loudest whistle. If none of the above work, you can try the next two steps.
Cutting/sanding your fipple
--If you've tried the above, you can try sanding down the end cap a bit more, and adjusting a bit the sides of the cut barrel portion. If you can't blow the whistle at all, this is definitely the area you need to fix.
Cutting lip/hole larger
--If you've tried the other things, you can try cutting your angle differently on the lip.