Question on Vintage Air Center Vent Install

[AusTx68]

My Vintage Air install has been a long time coming. I've had the system since last summer but I'm only now getting it installed. Everything is in except the center vent. I didn't install it because I decided not to use it. That decision was based on another truck I saw that only had side vents and routed the other to the floor, bi-level style. Now that I have everything installed, I changed my mind. Using the VA provided template, I used tape and a sharpie to mark the cut. When I was done, I compared the vent to the cutout and realized the hole is not wide enough. The mounting holes in the vent sit wider than the template cut. What's up with this??