There was a little bit of adjustment available when I mounted the latch. At first, mine was doing what yours is doing. Try loosening the mounting bolts and adjust the latching mechanism. If you recently had the hinges and seat hook off, you might want to make sure you lined them back up correctly. There's a little wiggle room on all of them. After I loosened everything up and retightened it, the seat went down correctly and latched right. It doesn't matter how hard you close it.
Patrick