@Judy-Elizabeth-Wilson super cute style! Really fits the children's book market, if that's your aim. Love all the little details!
Going to agree with other comments: it feels like it needs some "quiet" areas. Here's why:
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Where will the text go? If this is meant as a portfolio piece to show how you would illustrate a picture book, a potential client will probably wonder "where will we put the text?" If you fill every corner of an illustration, an art director will wonder if you know how to leave room for text, which is crucial. The bottom right would be a nice place for the text, in the grass, if all those flowers and bunnies and bugs and birds and minor details were removed. (Could the bunnies be grouped more near the door, as they would be for a party?) And keep in mind, there will be at least a 1/2 inch margin to leave room for bleed and hands holding the book. And text often takes up way more space than you think it will -- you may want to test out some text placement options or even some sample story text (at least at a 14 point) to get a feel for how much space text takes up and how to design around it.
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Where is the focus? A client will want to see that you can make a main character stand out. Right now, she's standing out because her hair is the darkest value in the piece, but her dress is blending into the background (which is not a good thing!).
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Is there too much storytelling? A ton of detail can be a great thing -- it adds so much to an illustration and kids love little details. But having so much going on can also take away from the main story being told. Use color, value, design, and shape to make sure the main story is the main thing going on in the illustration, and secondary stories are visually given secondary importance.
Here are a few things to try:
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Zoom out or stand far away from the illustration to view it as a thumbnail size. Is the story still communicated? Can you clearly see what's going on in the illustration? Seeing an illustration from a different point of view can help you pinpoint what's working and what needs improvement.

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Take away all those colors and view it as a black and white image. Does the composition still work? Is there a focal point? Is the illustration clear? Has taking the color away changed the storytelling? What stands out? What fades away? Are there high contrast areas of light and dark, or is everything mostly mid-tone?

These aren't my own ideas -- they're things Lee White and Will Terry always recommend in their critiques. And they work!
One last funny little nitpicky thing: the unicorn's tail looks like it's growing out of the princess's dress. What if you extended its behind so it's clear that the tail is connected to the unicorn? It might also help the princess stand out even more.
Hope this helps! And please, if you end up making changes to this piece, share the progress. We'd love to see it!