Poor you; I had that happen several weeks ago...we sat for 3 hours!!
I talked to my vet that night and they told me to put sit with him and put pressure on it. I even put his foot in a box of cornstarch. Styptic powder didn't even work. Just apply hard pressure for about 20 minutes and you should get it to stop.
I heard that baking powder also works if you don't have styptic.
Once you get the bleeding to stop, if he runs around again, it may start up. This is what happened to Zoe. She bled, was okay, and the next day a the beach, she bled again. But after that, she was fine.