I am having some issues keeping the knife flat on the stone as I pull it from left to right on the USB. I don't seem to be able to feel the stone through the knife so I wobble a bit and put facets on the edge. I am not pressing down hard and have watched a lot of videos on the technique but still I seem to wobble while pulling the knife across the USB. Is there any kind of technique that I should be developing as this is getting a little old.