It's probably fine. Bike rear stay vary tremendously bike to bike with some being very stout and some more pliable. There's also a difference in the bending properties of various metals and tempers. Mild steels spring a very short amount before bending, alloy steels can be very springy, resisting bending and returning to original dimension even after flexing a decent distance, yet once they start bending it's easy to go too far.

Once you've got it where you want it, it'll stay that way until there's enough force to exceed it's flexible range and bend it anew.

BTW- next time around try to control the way you cold set (bend, in fancy terms) the stays so only one moves at a time. Then you can take each half the distance, and make sure the center line is maintained.