I'm not sure I would trust the accuracy of the machine setup given you have the work piece extended beyond the recommended length without support. Most manufacturers recommend the work piece be supported when extended beyond 3 to 5 times its diameter. Beyond that length even minor tool pressure will cause the workpiece to deflect. Your measurements seem reasonable, but may be due to the fact the tool is deflecting the workpiece rather than cutting it.
Here's a link to an article on setting up and running a lathe from the American Machine Tools Company.
How To Use a Lathe (americanmachinetools.com)
Here's a clip from that article. It's near the end in a section entitled "Turning Work In Chucks".
"Some work can be machined more efficiently by using chucks, collets, mandrels, or faceplates to hold the work. Rough and finish turning using these devices is basically the same as for turning between centers.
The workpiece should not extend too far from the work holding device without adequate support. If the work extends more than three times the diameter of the workpiece from the chuck or collet, additional support must be used such as a steady rest or a tailstock center support. "