Taking limbs of your bike when trying new tricks happens to lost of people.
When i was still riding pegs, i would always take my foot off on Feebles and other grinds, because i thought i was going to mess up, i named the syndrome of taking limbs off unintentionally "***** Foot"
I cant barspin, but i can tell you that if you just stay on your bike you will have a better chance.
Also as dumb as it sounds, try barspins and other tricks like that on Scooters, it actually helps you, and its weird. I tried no foot cans on my scooter and now i have an easier time doing them on my bike(i dont have them down yet, but i can throw them faster, and usually land on my seat)