Set width of section title

Question

I try to prevent section titles of breaking "too early", i.e. leaving so much room between it and the page border.

Like in this screenshot, I would like the "system" and the "digestion" to be in the same line as the rest of the titles.

I am using the scrbook class.

This is some code reproducing the problem:

\documentclass[%
   final,      
   11pt,
   bigheadings,
   a4paper,
   DIV11,      
   1.1headlines,
   headexclude,  
   footexclude,  
   mpexclude,    
   pagesize,     
   twoside,      
   onecolumn,    
   openany,      
   titlepage,    
   halfparskip*,
   headsepline, 
   nochapterprefix,
   bibtotoc,       
   tocindent,      
   listsindent,    
   pointlessnumbers,
   fleqn,           
]{scrbook}

\begin{document}
\section{This is a long section a long section a long section title}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam ultrices, lectus vel    rhoncus ornare, dui neque rhoncus lectus, ut eleifend risus erat et nibh. Cras accumsan volutpat est. Nunc cursus augue non mi tincidunt pretium. Aliquam et eros mi. Curabitur eu dui est, sit amet laoreet est. Nullam libero nisl, convallis eu placerat eu, pellentesque sit amet est. Suspendisse dolor mauris, porta non venenatis nec, eleifend nec erat. Aenean hendrerit volutpat quam. Vestibulum fringilla magna pretium mi pellentesque lacinia.


\end{document}

Answer 1

You're using a large number of obsolete class options. The specific one in question causing your problems is halfparskip*; instead use parskip=half*. I've updated your MWE with the obsolete options removed:

\documentclass[%
   final,      
   a4paper,
   DIV11,      
   1.1headlines,
   pagesize,     
   twoside,      
   onecolumn,    
   openany,      
   titlepage,    
   headsepline,
   parskip=half*,
   fleqn,           
]{scrbook}% http://ctan.org/pkg/koma-script

\begin{document}
\section{This is a long section a long section a long section title that spans two lines}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam ultrices, lectus ver
rhoncus ornare, dui neque rhoncus lectus, ut eleifend risus erat et nibh. Cras accumsan 
volutpat est. Nunc cursus augue non mi tincidunt pretium. Aliquam et eros mi. Curabitur 
eu dui est, sit amet laoreet est. Nullam libero nisl, convallis eu placerat eu, 
pellentesque sit amet est. Suspendisse dolor mauris, porta non venenatis nec, 
eleifend nec erat. Aenean hendrerit volutpat quam. Vestibulum fringilla magna 
pretium mi pellentesque lacinia.
\end{document}