You have run into a resolution problem.
Increase your magic wand setting for more facets.
Then remake the profile.
Perhaps trussmaker doesn't do curves well - I don't use it much.
Profiler is an option.
Alternatively:
Try to make this beam with a curved wall.
Walls have high resolution in curves.
If you need a round tube, use the log wall tool.
Set the log diameter to your tube diameter and space the logs beyond touching. Make a wall only as high as the tube.
Dwight Atkinson