Congratulations that you applied the law of attraction successfully already! All that visualizing sounds like it should be having a great effect.

The method to use the law attraction is like you are doing it: You use imagination to change how you feel, which will in turn change the kinds of situations you find yourself in. You are absolutely right, your thinking after you completed your exam will still affect its results- for example, your thinking will cause a telepathic connection with the person correcting it and will nudge that person wherever that person has wiggle room to make a call.

When you don't appear to be able to use change your feelings with imagination, it means that you "hit a snag"- your new feelings contradict the ones that are caused by an existing belief. All law of attraction methods I have ever seen are two parts: One, visualize what you want to change your feelings. Two, uncover existing beliefs when they contradict you.

My favorite method for uncovering existing beliefs comes from Bashar. Is is very similar to Abraham's method, which is to simply ask yourself, when you have persistent negative emotion: Where does that come from? Bashar's method takes it a step more technical, which I think makes it work better. You ask yourself: What would I have to believe in order to feel this?

You can do this informally, but you can also get a little bit more involved and specifically sit down, bring up your worries feeling until it is very strong, notice a lot of detail about it, where your body feels tense, whether the pain is dull or sharp and where, and once you feel you have grasped every part of that negative feeling, you ask yourself, with as much authority as you can muster: What would I have to believe, in order to feel this?

You will most likely get a vague answer. Keep digging until your answer is a clear, simple statement- repeat the question until the answer is clear enough for you. Once you have done that, you're good- the process is over, the belief is no longer active. Go back to imagining the things you do want, which in this case would be the positive exam results even in those subjects you were previously worried about. Enjoy that the energy now responds much better to your visualization. If you run into another snag, even one that is similar to the first, don't worry- that's normal, beliefs have lots of layers if they've been around for a while. Just clear each one individually and your snags will get much better, and you will notice by the feeling effect you get from your visualizations.

It really sounds like you got ahold of using the law of attraction to your advantage quickly and well- do find a lot of further great things to create! Have fun. And enjoy the snags too- one might say we have chosen this world particularly because of them.