Been there done that! Luckily canceling a crop while it’s growing is easier than brewing moonshine (although not as tasty)!
Here’s what you do:
1) Open up your move menu (arrows on the bottom right of the screen) and tap on Cletus’s Farm:
2) Once you’ve selected the farm it will be highlighted in green (or red). Tap the cardboard box (inventory) and select the blue Store button:
3) Next open up your inventory (accessed via the build menu & again the cardboard box) and tap on Cletus’s Farm and place it back where it was.
That’s it you’re all done! Now you can get back that high quality moonshine!