I put a fresh clutch in my bike and was unable to ever get it to disengage the tranny. I ended up to were I got just a little when it was warm, now that is a bit more worn it works great. You may need all new plates and springs if something is actually seized in the clutch, or possibly the basket is worn and it is preventing the plates from separating. Or the clutch is tight. Since I had checked all of those things on mine, I just got it rolling before putting it in gear and then would sometimes (not often, or very much) pull the lever in part way and rev the bike while in gear to burn the clutch a bit and break it in. Works great now, though when cold it still won't disengage. But after a half a mile when the oil heats up and the clutch gets warm it works great. If you are really worried you can take it apart and check for problems and wear. That might not be a bad idea anyways since you got it for 400.00.
And definitely work on limiting the use of the shift key. :)