Try to take with a higher exposure. 1/20" may b a bit too slow which may caused some of the blurs. Try using 1/50" for ur 55mm zoom. As mentioned by Silence Sky, ur subject haf to be sharp. Use single focal point for panning, then follow the subject n snap.
From your picture, set ur focal point to the 2nd last on the right side of ur 300D. Ur background is blurred enough, which is alright. So u haf to focused more on capturing ur subject~~~ Try using Tv/S mode instead of Av/A mode. I feel that ur pic may b a bit underexposed, try having a +0.3~0.7EV.