Doubler strip
This has been discussed before. In the past, when someone has dimpled the spar and countersunk the hinge, Van's has recommended fabricating a doubler strip to go behind the hinge with just drilled holes (not dimpled nor countersunk). This will be the 4th layer of material (i.e. skin / spar / hinge / doubler). Without the doubler, the hinge will be likely to curve during riveting because the aluminum is soft.
Good luck,