Cut and close at an angle

 From:  Lara (MALA)
11938.1 
Hi, I have the backrest of an upholstered chair here. For formal reasons, I would like to cut the front ends at an angle so that they match the furniture frame.
Now I have cut the round shape at an angle. When I finish it with “nSided,” there is no clear angle (20°) left. As you can see from the side.
How can I solve this better?
Best, Mala