When photographing in dim light, it's harder to see if the camera has got the focus locked in the right spot. It's also harder for the camera/lens to find the focus in dim light. It looks like it's a bit sharper in the background on the wall lamp and mic stand, but i'm not sure. With a shutter time that long, it can also be blur when the artist moves. I like the image anyway. Just take a lot of images and then keep the ones you like the best. Have a big memory card and use the continues shooting mode on the camera..
I can see that you used ISO 3200, still the shutter speed was very slow (1/5). Even if you have image stabilization, the image can be a bit blurry. It's often useful to have a tripod or at least a monopod, but you can get sharp images without support. Putting the left hand under the camera and the left elbow in against the body to your hip usually do the trick. Getting a faster lens is also a solution, but an expensive one...
I think you will be happy with your choice of camera and lens. 60D seems to be a great camera. I have never tried that lens, but it's nice to have a lens that covers that zoom range.
It will always be a compromise with that kind of a lens and the sharpness will often be better with a lens with a shorter focal length or a prime lens. If you need a lens that is much faster and if you can get pretty close to the stage and doesn't cost a fortune, you should consider canon 50mm/1.8. It's not rugged, made in plastic, but it's sharp and it will let you take pictures in low light. It's small so you can probably have both lenses with you. It's also a nice portrait lens. Just remember that the depth of field will be really shallow when you use it wide open at 1.8 or close to that.
Good luck.