There are two rules to follow when trying to figure out if you’re using the correct size screwdriver on a screw.
First, go from large to small not small to large. You should select the largest screw driver that still fits in the screw, rather then going from small and trying to figure out if you have a good fit.
Second, if you have quality screw drivers, the fit should be tight. Without having to force the screw driver, the fit should be close tolerance enough where the screw can support the screw driver without even having to hold it: