you might have gotten a defective one, but don't expect it to be a simple finger-fit thing .... the reason those plugs are 'inflexible' is cuz they're a rubber coating over a piece of steel, and any I've dealt with are a hammer fit ... get one edge into the hole with the plug fairly flat - tap the higher side so the low side is tight on the flange - hold it there and use a dull slot screwdriver to force the bottom rubber edge down until it's in halfway round or more - hammer the high side over and down .... after a few times opening it, the task gets easier, but a hammer is still needed
Bill
