In order to get the background more white you need more light or more exposure. Try using a tripod. You can even make one light do the work of many. With a small aperture and a long shutter speed, you could actually move one of the lights around so that it covers more area.


However, the best results will come when you are lighting the background separately from the object. The way you have it here, any shadows created by the object are cast onto the background. If you put some separation between the object and background, you'll be able to light the two somewhat independently of one another and get results that are closer to what you want.