Cunobelin's diagram is for a threaded headset, which I don't think you have. Loosen the top cap and make sure that it is tightening on the stem and not on the top of the steerer. The top of the steerer should be below the top of the stem, and if not you need a spacer in there. That's assuming that the fork is the right way round in the first place and not trying to correct itself.
In the OP, the image clearly shows a threaded headset with the lock nut and top cup clearly visible