With the Plane set to visible, as yours is, click on the Plane in the tree. That will highlight it in the graphics area, and place a blue ball at each midpoint and each corner. Grab one of the balls on a corner with your cursor and drag to re-size.
You can also right click the plane in the design tree and choose auto size
If the plane is already set to Autosize, then you probably have some errant sketch geometry or part way off in space.
The Autosize feature is amazing. Thank you guys.
I actually had a screw out in crazy space which was the cause of my extends stretched so large.
Thank you for all your help!