To make sure you don't stress the aircraft:
Be absolutely certain that during the spin you hold the controls deflected to their stops, to avoid getting into a spiral.
Install a G meter somewhere inside the cockpit, you can get them reasonably cheap second hand
This should relieve your fears in making sure you don't overstress the structure
There is one imponderable, as many pilots are flying club aircraft, and if it is spinned regularly, there is no way to ascertain that it was not abused. However I have never ever heard of a 172 losing it wings...
Go pratcise in an aerobatic aircraft, it has oversized controls optimised for slow flight and spin recovery and it withstands loads up to 6 g's