I had the same fear. After 3 months of really bad sugar levels, I finally tried it. It didn't hurt. It's impossible for it to just fall off. It takes 5 minutes to rip it off. Also, painless. I'm a coward who hates pain. I've been through cancer and chemo. I still fear shots and needles. Libre 3 is 100% painless. It's silly looking back now that I use it everyday. It's fun actually. It might sting afterwards for a few minutes when you apply it. You don't actually insert it. It shoots into you. It's not a needle. It's a tiny flat plastic wire that pops into from the weird cylinder thing It won't get knocked off. trust me. Good luck getting it off the first time. Same fear, but it's glued and the sensor will not hurt. Just rip it off.
If you need it, use it. It's all inside your head. It's painless and so freaking easy. I avoided it for months out of pointless fear.