I vote to keep the bump. NOBODY will know the bump is not really needed unless you tell them, and the fill piece seems to be already cut for it (You have to weld up patches either way). You went to all that trouble to replicate it, but it also keeps that "stock" look when painted. JMO. But it's your car, your money, your effort.
Nobody sees it unless the trunk is open anyway and it also offsets the slightly angled blend where the lamp goes underneath.
But, with that in mind, and I know how detail-oriented you are, maybe try this to help make up your mind...
Take a flat piece of sheetmetal and hold it up where the filler would be to simulate the flat section. My eyes are old, but I seem to see a slight rise in that pinchweld area where the trunk seal would go. A slight arc upward, if you will. May simply be a visual angle or something, or a slightly sagging center since it's just being held up with magnets and not attached yet.
The pics below should give you an idea of the ability of that bump to distract your eye-line. The bump must work in that regard, since nobody else mentioned it. Unless, of course, you have another plan.
1 and 4 seem lower than points 2 and 3 showing a very slight upward arc from point 1 of the GM side of the rear panel that seems to go back again as you reach point 4. At least in my eyes. And, if I had to bet which one is laser-straight, it wouldn't be GM's side of it.
🙂
At this angle, it doesn't go away, at least for me. So I don't think it's just a Jedi mind-trick. Area 1 still looks lower than 2.
This is no way no how a knock on your skills. I think the filler looks unbelievably great. You just out-did GM's structure-work by a mile, so I'm simply pointing out GM's shortcomings on this. I wonder if all of the A/G-bodies are like this?