The KX is quite capable of handling as much film as the canister will hold.
How many turns before the film is back in the canister? It is possible that you were not winding on...
- Advance the wind lever before loading the film. This resets the rewind button release button on the base of the camera
- When loading the film, make doubly sure that the drive sprocket engages both the top and the bottom of of the film. (The sprocket is what actually moves the film.)
- Wind on at least one full cycle before closing the film back
- Close back and wind until the film counter is at frame one and confirm that the rewind crank rotates to indicate film travel
If the rewind release button is in the correct position and the film is engaged top and bottom but the film does not wind on, the drive mechanism is not working properly. This may be repairable by your friendly local camera repair shop or you can send your camera to Eric Hendrickson at pentaxs.com. Eric does excellent work at a very fair price.
Good luck!
Steve