Wow...definitely don't eat it. :/

I say if Bullfrogs are native to your home then what is the harm in releasing it. If the store you bought the tadpole in was local that could mean that they caught it wild in your area or What do horse people know about frogs anyway...?

You could always return it to the store, I'm sure, unless they don't have some sort of policy about that. Maybe there is someone in your area who has bullfrogs and could take it off your hands? I would put up a "for sale" thread and see if anyone is interested. You bought the tadpole so please be responsible about what you do with it. It would be sad to see a life wasted on a impulse buy. Just please don't kill it...