getting those springy body panels back

[Speedy88]

So I had to bend the lower part of the wing to get to the rust behind, but now it's kinda buckled and bent. It looks ok to the general eye but it's really annoying me now. But a hammer does nothing as the wing metal is kinda "springy". Meaning bashing it doesn't really bend it, just scratches the paint. I don't think a wooden block would do much more sooo any ideas?