From my experience, Law of Attraction is a Law much in the same way as the Law of Gravity, or Law of Physics. You don't need to believe in them they just happen. Even if you don't believe in physics you will still get hit by that bus coming towards you. The Law of Attraction states that you attract into life that which you focus on, believe in and think about. It's not a question of belief, it's only a question of how much you notice the law working.
As for the question: Yeah, your obsessive thoughts will affect reality, but they already are. Becoming more aware of your thoughts is all you need to do, which leads to gaining control over them in the long run. Scattered thoughts and focus don't manifest anything strongly, and if what you are anxious over is rather mild then there it doesn't matter anyways. What David said was spot on though: focus on the OCD, and let the Law take care of itself.
Work on pruning your thoughts and the garden will blossom how ever it wants to. Just without weeds for a change.
