If it were just the off fitment on the ends, then I'd say it could be the mounting brackets on the back being tweaked, but it looks flat across the front too.
Back in the day they used to have bucks to straighten mild damage/bends, but I doubt any shop nor dealer has them anymore.
See if you can find someone in your Indy area with a proper fitting bumper to compare it with front & back.
If it's off, then you may need to return it & look for another one.
PSS - Also check that the bumper's mounting brackets on the back are straight & correct angles, & not tweaked, as well as the mounting points of the front wall of the body/trunk.
PS - it also looks like the line of the headlight eyebrows & hood/lid are consistent, but that the fenders sit +/- 1/4-1/2" proud of them in the 2 pix below (passs. side seems most out), so there may be a bodywork issue making the bumper seem too flat in the center. However, it could also be an issue with the headlight & eyebrow adjustments too - at least in part, you should check alignment of all hood/lid, fenders, headlith covers/brows from the front dead-on too. Also do the bumper to bumper comparison with your & the know proper fit bumper off the cars - & you might also try test fitting yours onto the other 914 as well.
Good Luck!
Tom
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