Aaron, you can't just drag the end point of an arc. You have a couple of alternatives, though. You can select the arc and use the Scale tool to move one end of the arc. If you stretch a circular arc you end up with an elliptical one. If you can start with a parabolic arc, draw a Bezier curve set to 2 degrees. Then you can select the curve, right click and choose Edit Bezier curve and move the end point as desired. Because Bezier curves can be drawn in 3D, I would draw the curve on a large face if I wanted it to remain a 2D curve.
Irony: The opposite of Wrinkly