To turn a design on the lathe accurately, you should make a RevolveGuide.

Make a duplicate of your revolve. Rename it ["PatternOriginalFileName.des"]

Open your turning profile.

Suppress the revolve in Features.

Make the profile sketch active.

Add a vertical line to the top of the profile closest to the axis. Hold the shift key to make a straight line.

Add a horizontal line from the top of the above line. Make it 20mm for a pen revolve.

Do the same for the bottom.

Add a vertical line from the bottom corner closest to the axis. Hold the shift key to make a straight line.

Add a horizontal line from the bottom of the above line. Make it 20 mm for a pen revolve.

Connect the two horizontal lines. It should be easy if they are the same length.

Delete the part of the profile between the two horizontals.