All of that sharpening you've done so far has created a little burr on the back of the blade edge. If you run your finger up the back of the chisel, you'll feel it when you get to the edge.
To get rid of that burr, you'll need to flatten the back of the chisel. To do this, start with the 800-grit stone. Lay the back of the chisel against the stone and make several passes on it. The chisel must lie completely flat against the stone.
It doesn't matter how much of the back you place on the stone. You only really need the very end flattened, but the more you have on the stone, the easier it will be to keep the chisel flat.
Do several sets of passes as you did with the blade, moving up through the 4000-grit stone.
There. You now have a finely-honed and powerfully useful tool. Now go to this instructable
to see what you can do with it!