You might have got there already and just not realised it
Once you are getting a good ammount of smoke from the spindle, and the notch is filling up with dust (the darker the better) you want to ease off the pressure slightly and speed up the strokes - and do at least 30 strokes (1 stroke = back and forth).
When you take the spindle away it may well look like all you have is a pile of black dust, but the telltale sign of success should be a thin wisp of smoke still emanating from the dust-pile. If you blow VERY gently on this pile, you should hopefully blow away the surface bit of dust, and see a glowing ember underneath - this is usually no bigger than a pea - it might be much smaller.
Transfer this carefully into your pre-prepared tinder bundle, hold it up wih the wind at your back, and blow through the bundle until you get more smoke, which turns yellow, then a flame!
For more info, have a look at
http://www.pyrology.org.uk - especially the bow drill and tinder pages.