Welcome to the challenge Lydia. You got the shot, posted it to the challenge and didn't break any rules so I'd say you are off to a great start :-)
A couple of points. First, the dimensions of you image are huge. It is recommended, though not a rule, that you scale your image to about 800 pixels wide or tall.
This helps to preserve sharpness and detail when compressed to within the 150KB limit (which is a rule). For an image this size, you must have used a high level of compression and it looks like the detail may have suffered.
I am by no means an expert but to my eye it looks like the image would also benefit from a touch of levels and sharpening in post processing. Attention to post-processing seems to be a common theme in many of the winning images.
However, congratulations for getting an image in and I hope you enjoy the challenge.