Well i think that you problem is that you try to hard, don't be obssesed, just let it happen. When you say the affirmation do it like you are trying to hypnotize your self, don't concentrate on the words, concentrate on the meaning.

Also take a look at this page and be sure to do the exercise for "remembering to carry out your inttention"
http://members.aol.com/Aarenka/vision.html