I think so. If this is right, and you can see fork steerer poking out ABOVE your stem, then when you're clamping the top cap down, all your doing is squashing the steerer and not clamping anything. You can solve it by as said stacking it up more underneath, or trimming the steerer about 5mm. Bare in mind don't cut it too much so theres nothing for the stem to clamp onto, but you need to take enough off so that its well below the top of the stem. Take into account the thickness of the topcap itself too!