Hi Marco,
indeed it look that smal correction may be needed for that resolution.
My fast ideas by now are....
- Grab top-right corner (dotted triangle icon) and resize window a little bit

- In JCE editor (Admin) > Profiles > Default > Features & Layout (tab) > Statusbar Location: None and
check if you have "Allow Horizontal Editor Resizing: On". Then as last step remove icons that you don't need and keep only 2 or 3 rows, not 4 as is default from toolbar.

Then all buttons should fit perfectly.
BTW
In JCE Pro there is no "Powered by JCE Core...." bar and there is no problem ;) more space, but as you saw you can safe some space easly.