Getting the right frequency from an oscillator circuit
Your poor little op amp is trying to drive loads below 10 ohms, and it is not happy. Try multiplying R1 and R2 by 1000, and dividing C1 and C2 by 1000. Furthermore, you need to actually look at and understand your op amp data sheet. Take http://www.ti.com/lit/ds/symlink/ua741.pdf as a source. Look at figures 6 and 8. Do they tell you anything?

As a rough estimate, the open loop gain of an op amp should be 100 times the closed loop gain at that frequency. Since your closed loop gain is 3, this means the open loop gain should be around 300 at 20 kHz, which in turn says that your gain-bandwidth product should be around 6 MHz. It can be, oh, half that if you're not too picky about accuracy. Do you see this happening with a 741?

As for distortion, well, first you need to get the frequency response up. Then try the really obvious step: Wikipedia. http://en.wikipedia.org/wiki/Wien_bridge_oscillator. 

In the future, please do even a minimal amount of research before you come asking for help.