Sometimes it just happens. You could have had the enviroment perfect, and the snake just cant pull it off.
I had a male that was kept in great conditions, we watched carefully everyday, kept his humidity right on par, let him soak, but he had the WORST shed ever. His whole back was left, and it took both me and my BF to get it all off the next night.
It's okay to take the stuck skin off, it will be weird at first, but when you let them soak long enough, that skin will just slide off.
Most BP's are head shy, but I have noticed that when I help them shed, a switch turns on in their head and they will attempt to complete shedding right there with me. My male with the particular bad shed allowed me to rub his head and remove any stuck shed this way because he was (in my book) in "shed mode".
I find that slow gently movements from behind their point of view is the best way to go about it. I use a wet wet warm cloth and just slowly but deliberatly press my palm or thumb on the top of his head. He may jerk and try to get away for some time, (I've gotten a bath from them too) but eventually I can get it off. Either from the continued application of water and gently applied stroking, or from them finishing it in my hand. I find it's easiest to do it by myself with no one around to move and freak them out. I hope that all made sense!