Chances are your DS clock is off, since you got all the other steps right.
Go to settings in your DS and make sure it's set past 20:00 (8 pm)
Time changes twice per year, so there's a chance it's still set to 19:00 (7 pm) from the past time change. Let me know if this helps!
If it doesn't, double check you got the right held item. There are multiple Razor items in the game, so make sure you got the Razor Fang :)