Hi Lara,
""""""Did you use the cutting cube in one of my previous files? I guess no. Yours has an perpendicular cut. But thats not the right angle...""""""

No. My post was not a solution. I was responding to the post where you asked "why" this was the case and you noted that the opposite sides matched.

I created an illustration to show "why" and how you can't do it with a fillet/chamfer or "winkle"....

Sounds like Barry is bringing an understanding and solution...