I am going to present to you a little exercise that I hope will give you a glimpse into the mind of a real classical composer, the one you might become if you play your cards right. But first, you must clear your mind of certain misconceptions.
Classical music is about ideas. But you don't hear the ideas themselves -- you hear metaphors in sound that guide you to the ideas. You must rid yourself of any notion that your goal as an artist is to present lush sensual effects, or melodies that tug at the heartstrings. Those are simply means to an end, and if you don't have an artistic end, you are merely producing banalities.
Music is non-verbal poetry. It conveys to the listener an idea that cannot be described. I'm going to suggest an exercise now that should guide you into habits of thinking that will help you blossom into a classical composer.
Let's begin by composing a stretto. A good stretto is a "eureka!" moment for the listener. This will be the hard part -- if you can manage the stretto, the odds of your composition becoming a success are good. If you are unfamiliar with the term, here's how I like to define it: a passage in which thematic material is presented in counterpoint with itself, in such a way as to reveal hidden contrapuntal/harmonic potentials in the material.
To make this work, you should first choose a contrapuntal potential that you think your thematic material ought to possess. For example, your theme might be capable of being superimposed on a half-speed version of itself (augmentation) in such a way that new, unexpected contrapuntal/harmonic relationships emerge between the two voices. Then you must begin to experiment with a theme (or fugue subject -- since you are going to the trouble of writing a stretto, you might as well write the whole fugue. You may or may not incorporate it into your final composition, but it will be a treasure trove of ideas to draw upon.)
The challenge here is to find a theme that is melodically appealing, but also can perform the contrapuntal task you have assigned to it. I have found that the first pretty melody that comes to my mind is generally useless -- it takes a lot of experimentation and modification to tweak it into shape.
Your goal in crafting this stretto is to use it for that "eureka!" moment in your composition, analogous to the punch line in a joke. The rest of the composition is the "set up" for that moment, or progression of moments.
So, let's work with the theme you have written. Introduce it, at the beginning of your composition, just as a melody. Don't present it in counterpoint, just give it an attractive harmonization. Seduce the listener with it. Let the listener think it's all about the pretty melody. The opening of a good fugue is like that, as is the opening of any work of classical music (all classical forms worth their salt, including the sonata, are derived from the fugues of J.S. Bach, the great Moses of music.)
Now, as the composition progresses, your theme will be like Clark Kent, going into the phone booth and emerging as Superman. But not all at once -- think of Clark doing a strip-tease, revealing his powers bit by bit. You can vary your theme in any number of ways, by introducing a second theme and then combining the two contrapuntally, or by re-harmonizing your theme, presenting it in different keys, in the relative minor or major, the possibilities are endless.
The key thing to remember here is that your theme is being progressively revealed as something that is not merely pretty, i.e. appealing on a sensual/emotional level, but also meaningful, conveying an idea that is cognitive/spiritual. That idea will be communicated ironically, as the listener compares the first, naive version of the theme with the later, more potent presentations of it. And the real content of your composition is not the theme, or any particular moment in the composition, but the transformation of the material that takes place, and this transformation is not "heard" in the ear but rather in the mind.
When you have finally completed a composition that you believe can evoke that sense of "eureka!" in the mind of the listener, subject it to the acid test. Imagine that you are a pupil of Johannes Brahms. When he reads your composition and it unfurls in his mind, will he frown, and then mercilessly expose the weaknesses in your effort, saying in conclusion, "Do not amuse yourself further in this way!"? Or will his eyebrows slowly ascend as he recognizes that there are real ideas in your composition?