Not necessarily, but I’d be surprised if the demo saddle fit your horse perfectly with no adjustments. At the very least I’d expect the rep to have a conversation with you about it. When I took mine on trial the rep adjusted the tree and then made some flocking adjustments to fit my horse so we could really get a feel for whether he liked it or not on trial. We still ended up pinpointing a few more minor tweaks, but it fit well enough on trial that I was comfortable purchasing it and going from there. There were a few saddles I tried that my rep wouldn’t even let me sit in for more than a few minutes because she didn’t like how the demo models fit my horse, and with every saddle she pointed out the things she liked and didn’t like and what she would change to fit him specifically.
Are you still using your half pad with the new saddle, and does the rep know that? That would be a red flag for me unless there was an explicit acknowledgement that the half pad worked well enough for a demo and they’d adjust the saddle once you’d decided to keep it. If it’s just one or two tree sizes too wide that might make sense.
Unfortunately not all reps are created equal. It’s hard to tell from the info provided but it sounds like your rep may be focusing more on selling you a saddle vs fitting one to your horse. If you really like the Prestige it’s probably worth getting an independent fitter out to take a look at it while on trial just for peace of mind, or at least getting a second opinion from your trainer or another experienced horseman.