If a line after the last line that features a hyphen has too large word spaces, you can adjust the hyphenation manually with soft hyphens (also called smart hyphens). You can use the menu entry insert > character > smart hyphen or its ctrl + shift + - shortcut. Or you can remove hyphenation locally. Select the text for dehyphenation and run Extras > Dehyphenate.
Also, If you want to squeeze some text, select it and set horizontal scale to 94-98%. This works with most text-sized fonts. A difference between normal and condensed script cant't be seen.
With 1.3.4 you can create manual line breaks, so that if the word starts with a soft hyphen, it does not hyphenate.
Further reading about Hyphenation in combination with Full/Forced Justification.