I agree with what's been said, but I'll also add a couple of things.
1. BP's can get tired of handling quickly even as established adults, depending on the snake. My almost 9 year old BP, Shayna, will tell me if I've had her out too long by tensing up a little too. They are shy animals and it doesn't necessarily mean you are doing something wrong, but that BP's like to be in dark places most of the time where they feel safe (like a borrow in the wild or a nice hide in captivity).
2. Going back to the shy point, BP's can startle themselves. Shayna, who has never struck at me or bit me etc. get scared of her own shadow. Sometimes, I'll be holding her, and she will bump into my arm or body on her own, and then shoot back startled and nervous. It's kind of a BP thing.
It isn't clear to me whether your BP bit or just got startled. Either way, as mentioned, time and gentle handling without overwhelming your BP, especially when young, will generally lead to a well adjusted BP. However, that doesn't mean he/she will never get startled.