Well, IMHO, if it is gone it is gone.... simple as that. You can steam a dent out sometimes & you can steam a warp up or down sometimes, but you cannot make the wood grow back & replace wood you cut out....
Unfortunately, you have a choice of living with it or adding a piece that will most likely be spotted right away & may look worse than the lowered part.
I try to measure 11 times, come back tomorrow & measure 11 times again, then cut once. And I never cut unless I have Just measured it again to be sure.
One time I was building a rifle & was very sick several times during the building process. Took me 18 months to build the rifle as I was on & off a couple time & sick in 3 mo intervals. Anyway, I had the buttplate marked for 6 mo probably & one day I just decided I was tired of looking at it & would do the buttplate. I cut it off, fitted the buttplate & went on.... I had no idea that when I measured it, because I was ill & misread the tape & actually measured 15 1/2 rather than 14 1/2" LOP. So I was down to the final 600 grit sanding before finish & I picked it up one morning & shouldered it & WOW, what a rude awakening ....... :redface: Being a extensively carved stock & engraved patchbox & all, there was no way or correcting this, so I finished it & sold it even tho it was intended for me.
So from then on. I measure over & over & over & over & etc.....