It depends on what you mean when you say "what you really want". You probably mean all of these things, from time to time.

Fake desires based on a negative belief

Sometimes, "what you really want" comes from a negative belief tricking you into thinking you want this, but in reality the desired thing has been carefully designed to be unobtainable, by the nature of it being negative.

For example, a negative belief might trick you into thinking you want "the thing that is right next to me". But, once you get the thing that is right next to you, you no longer want it, because it is no longer right next to you. This phenomenon is well known by various proverbs, for example, "The grass is always greener on the other side of the fence", or "You want what you can't have". There are entire industries built around people suffering from various forms of this condition.

The best method to deal with this is to continue to clear negative beliefs. Don't worry about losing track of certain identity conditions created by the fake beliefs- the beliefs may try to trick you into believing that you will lose yourself without them. The contrary is true- you were someone else all along, and the beliefs were obscuring that. Clear the clouds.

My favorite method for clearing negative beliefs is to use Bashar's method. Follow your excitement to the best of your ability with no expectation of a particular outcome. When your rising energy causes you to feel more, both good and bad, focus on a bad feeling and ask yourself: What would I have to believe in order to feel this? Keep prodding yourself until you get a sense you exposed a core belief. Once you did that, the process is over. If you don't believe that after exposing a negative belief it will be gone, start the process on the belief that negative beliefs are not gone when you expose them.

True desires blocked by a negative belief

When with "what you really want" you mean true joy, true extasy, to support yourself, to have excitement, to support those you love, to live in a high energy state, and also more specific versions of these positive things, then, yes, you can ask for very specific things.

If you are not getting them, it is most likely because of a blocking negative belief, one that would say: No, I can't have this, it's impossible. Or, no, I can't have this, I'm not worth it. Or, no, I can't have this, because then there would be negative consequences (there never have to be negative consequences to anything).

Here, too, the solution is to clear the negative beliefs. Another method I like to use comes from Huna, as taught by Serge King. It is called symbol healing. You imagine a symbol of the bad feelings- normally, you will like the symbol about as much as the bad feelings, which is to say, not at all. But you will have a representation in a universal langauge that your core vibrations will be able to understand. Then, you change the symbol, tweak it, fiddle with it, try different arrangements, until you experience a sense of relief. This is a somewhat longer process as Bashar's method, because you are actively constructing the positive belief, but it is more directed and active, which can feel very empowering.

Getting what you want blocked by your perception of not getting what you want

Finally, often enough, you are getting exactly what you want but you are too full of negative beliefs to actually get it. For example, you could be working with a pretty girl (provided you are a person who would like to have a nice relationship with a pretty girl), and that person likes you, but you start acting weird or negatively whenever you are around that person, but not otherwise. There could be any number of negative beliefs in this particular situation, for example, you could believe that some people are too good for you, or you could believe that you are unworthy of a nice relationship, and are supposed to get into a relationship with someone who is more negative, and so on.

Again, the answer is to continually explore and clear negative beliefs. I like Bashar's method the best, because it is so simple and quick. Symbol healing is also very powerful, so I would try it and see what suits you. A third message that I also got from Serge King and his Huna teachings is blanket forgiveness. This works best if you feel a type of negativity that is rooted in anger. You sit down with yourself, feel the feeling, and say to yourself, with all the authority that you can afford yourself at this time and a little bit more: Whatever this is about, it is forgiven. Repeat with various negative feelings until you get a sense of relief.

All of these reasons have one thing in common: The reason why things are not happening as you asked for them, whether specifically or as a pleasant surprise, are the negative beliefs.

Getting specific things

If it is important to you to get things in a very specific way, both my experience and observing others say you can do that too. I have somewhat abandoned that because it just got too complicated- I like the simplicity of just drifting around towards better and better feelings. But you can do it. Probably, as long as you still of lots of beliefs to clear, letting go of the specifics of wanting things and just wanting "something positive" is very helpful because then negative beliefs have much less leverage to trick you, so they are easier to get rid of. So perhaps being specific about desires is a good thing to do once you feel comfortable with a basic level of positivity.

I have found the best way to get specific things is called "Haipule" and it comes from Huna teachings by Serge King. It is considered a tried-and-tested method to create specific things in those circles.

So to directly answer your question: There are limits to how closely your specific desires can be matched, but you will always get the closest match possible to the energy that you put out. The fewer negative beliefs you have, the closer that will be to what you consciously want, and the more it will surprise you positively. Finally, the better you are and fine-tuning and controlling and working with your vibration, the closer the manifestation can match what you put it, if you want to do it that way. The more you do it, the better you get at it.