Did you have a Retul bike fit at P-X then, and not just some guy looking at you on the bike again? I am surprised they said it was the wrong size, rather than changing the contact point locations..
As alluded to above I don’t see why you’d need to change the bike. I think there’s a lot of b-s thrown around about frames fitting correctly- out of the box two bikes can feel very different even if they’re the same size, but you should easily be able to change contact points so they feel identical.
You’ve 3 contact points (well 5 really)- hands, bum, feet, and only the cranks location are pretty much fixed in space.
Whatever ideal position the fitter has calculated for you can almost always be recreated on any frame, unless it’s several sizes out. Whether it’s truly the right position for you is a different matter, but it’s a bit early for you be talking about changing the bike.
Rotate your hips forward, flatten/ straighten out your back, that’ll help. Build your core strength.