Over in the main GT7 & PSVR2 thread there's about 5 people who have mentioned this, possibly more. I'm one of them
Most obvious is the small hands and small steering wheel which look obviously toy sized, but also the other cars don't look full sized, it's oddly immersion breaking in terms of it feels like being in a very realistic toy racing game.
In terms of solutions, I have tried playing with the view position and changing the IPD setting which doesn't seem to have made any difference to the sense of scale. The correct IPD for me seems to be right in the middle of the adjustment range so I don't think I'm outside of the adjustment range.
I'd estimate it feels about 25% smaller than real life perhaps.
Had no such problem with the Oculus Rift in Assetto Corsa or any other VR game. I will have to try the PSVR2 in another game at some point to see if it's GT7 specific.
I wonder if it's somehow related to cockpit view settings in pancake mode? I may try the game without PSVR2 plugged in, change those settings back to default and see if it makes any difference!