I accidentally slip-stretched an audio clip rather than cropping it, and now the timing's wonky and it sounds funny. Is there a way to undo the slip stretch?
 

• If you haven't rendered it yet, just slip-stretch back to 0% stretch.
• If you have rendered it, no worries. When you render a clip, SONAR preserves the original in your Project Audio folder for the project (SONAR will also preserve the original if you render a loop or bounce a clip to itself for other reasons).

 
It may not be easy to find the original file, but it's in there. Use the browser to listen to the various files, but make sure Preview at Host Tempo is off so you hear the original file.

FWIW...   slip-stretching to change clip duration is Ctrl+Drag vs. a "plain" drag operation (no modifier key).   And as Craig wrote, if you haven't saved you should be able to Ctrl+Drag the right clip boundary back to the left until it reads 100% (no time stretch).
 
Edit: Oh..... and when time-stretching like this there will be a yellow line at the end of the clip during the stretch operation. 
 
 

The best way to ensure you've totally undone slip-stretching will be to set Stretch Amount to 100% in the Audiosnap section of Clip tab in the Inspector. The percentage display in the clip doesn't show enough resolution to ensure you get back to 100% and disable stretching altogether.