Tony hawks american wasteland question plz help?

i am on the downtown level and i cant complete the task with master zen i hav 2 get focus grind the loading dock and do a 360 hardflip over the dumpster i kept trying 2 do it and i couldnt land it and wen i finally did mr zen said nothing as if i hadnt done it plz help i want 2 get 2 the next level