There’s no way I know of to reverse the round corner operation. You have to make sure you are happy with what you have before confirming the change. An idea might be to save a copy of the original so that you can go back to it if needed. Hindsight can be an ugly thing.
I notice that the model axis have somehow become upside down. You can correct that by right clicking on an axis and choose “reset axis” from the context menu that appears.
The model units you have set are at 6 decimal places, do you really need that kind of precision? Maybe 2 or 3 places would suffice. You really need to enter precise units when doing any sort of accurate modelling, items like this will highlight every error even worse.
Looking at the image I can see that it does not seem symmetrical because of the diagonal hidden lines you have running across every other top face. Also when I try to copy/rotate one of the sculpted faces off what I believe is the centre the last one doesn’t match up.
That’s so far…