We estimated, based on texture and looks, that a piece of meat was cooked Kimachol Ben Drusoie and put it on the Blech. On Shabbos when we took the meat off, we realized that it was not cooked (the meat was very red), can we still eat the meat on Shabbos? We have other foods to eat as well for the meat course.
If you put it on the Blech before Shabbos, you may even put something which is not cooked Kimachol Ben Drusoie.
However, so long it’s not fully cooked, you may not put it back on the Blech on Shabbos, once you take it off.
(This principle applies to anytime you take off something from a blech on Shabbos).