My 36-inch walnut panel bowed on me halfway through a glue-up yesterday, so I clamped it against a straight steel bar overnight. | Cabinetmakers - Librear
Yeah, @michael_baker is spot on about that built-in stress. Forcing it straight is just a temporary band-aid. That internal tension is gonna fight the steel bar forever, and you'll likely get a worse warp or a crack down the line when the humidity changes. Honestly, starting over with properly dry wood is the only real fix here.
Forcing it straight with that steel bar is just asking for trouble later. Wood moves with the seasons, and that built-in stress will probably just make it crack or warp somewhere else. I'd cut my losses and start over with drier stock.