My fail was, i added a widget to the wp foro sidebar, i removed it now, but the width of the forum keeps like the widget is still there. I attach an image to show what i mean.
Hopefully you can help me to fix this issue.
Thanks in advance
This was a double sidebar issue. The red marked area was the wpForo Sidebar area. To remove it, go to Dashboard > Appearance > Widgets admin page, put some widget in the wpForo Sidebar and remove it to reset the sidebar cache. After this manipulation, the wpForo sidebar will be removed, and you'll only have the right sidebar which comes from your theme.