Poor control most often is mechanical and grip oriented. However, sometimes not thinking so much about things when you're out there on the mound helps, too. And what do you do and think about before the game and in between innings? What are you visualizing? Do you see yourself making "perfect" pitches or failing? Positive thinking goes a long way in pitching.
If you're still having trouble, talk to you coach about your mechanics, video tape a performance and sit down with your coach to review it, and pick up a copy of "The Mental Game of Baseball," by H.A. Dorfman. I've got a link to it on my "Books" Web page on my main website.
Keep us posted on your progress.