If the 4 vertices at the right end of the face are off plane, you can window Select just those vertices (points) and the use the MoveTool to “stretch” them back onto a plane.
But you might need to draw a working plane (a face inside a group.)
TIG has a WorkingPlane plugin to create these planar faces.
http://sketchucation.com/forums/viewtopic.php?p=274345#p274345
You need to join SketchUcation forums to download, but it is free.
Also ref topic thread:
We have guide LINES. How about a guide PLANE?