How do I fix the L-profile on the board ?
Place the L-profile on the board and using a drill press, drill a 1/8 inch hole  through the L and through 1 inch of the board. Then screw the screw in the hole with a hammer.
Place the L-profile on the board and using a drill press, drill a 1/8 inch hole  through the L and through 1 inch of the board. Then screw the screw in the hole with a screwdriver.