Q: How can you get your horse to stay next to you after you have fallen off of her?

Last night I was at a rodeo and i slid off the sadlle because she had spooked. She took off after I fell. I lunge her, and she does seem like she has respect, but is there a way to train your horse to stop after you fall? In the round pin when i say whoa she stops, but anywhere else she acts like she hasn't ever heard it before. Can anyone help? Thanks:)