I've had it for a while but haven't used it much because it is not sharp. Suggestions? Can it be sent off and is that expensive?
I would suggest 2 things:
1) Stopping down the aperture, try clicking pics at f/8 or f/11. This negates the use of a fast aperture lens such as yours, but it will point to the next step. By stopping down, we increase the DOF, and thus some focusing errors can be hidden.
2) Performing Micro-focus adjustment. Since you have not mentioned which brand camera you are using, this may or may not be available directly in camera. This should be performed by a knowledgeable camera technician, if it is not available in camera menus.
A third and very distant possibility is a lens focus mechanism failure.