Thank you for your post.
It's difficult to determine why this is not working correctly. First, make sure you install the appropriate print driver with the Zebra ZP 450. If you are using the 2844 driver, it may not be compatible.
Try creating a new label layout (do not duplicate). Add a couple of fields for testing purposes and go into Preview mode. Does this appear correctly?
In Print Setup, make sure the printing is set to 100%. Most importantly, make sure you have the correct Paper size.
Let me know if you continue to have difficulty.