I know it can be scary when you sign a waiver which tells what can happen in a worst case scenario. But you know they must do it for legal purposes. I don't know what percent of colonoscopies end with problems but I'm sure it is very small.
I had my colonoscopy a few months ago and it was a snap. They put me completely under and I have no recollection of any of it. I am 5' 4". I had no pain afterwards (kinda makes me wonder if they even did anything

. The only bad memory I have is of drinking the lemon-ginger phosphosoda which was disgustingly gross. I have to have another colonoscopy in 5 years and I am already dreading that drink! But the peace of mind you get when the procedure is over is worth it.
Good luck.