Ah I bet you're having the same trouble I had. You see, there's actually a second entrance farther down from that main one, down on route 16.
There's a trashcan that you can view from the top but you don't have access to. For some reason, this counts as one from the "main" area, where it should only be 3 (one near the entrance, one near the left, and one in the back by the Boss)
Go out, down south and enter that one. There's a few more trash cans down there. Also repel the fuck out of there or you'll end up getting Magnetons and Klefikis out the ass.
