Maybe you could have stopped cropping at 1600 x 1200 and submitted it at that larger size. However, you absolutely can reduce the size of an image without cropping. This function varies with the software you are using, but check for an "Image - Resize" menu. Typically, you can then select from various standard sizes with a 4 to 3 aspect ratio, or you can enter your own numbers for pixels of width and height.
By the way, at first I thought you had a typo in your title and meant Clouds FORM An Airplane. That sure looks like a fighter jet shape in the upper right, to me.

Always dreamy to look out of an airplane and see this. This is quite a good shot. :)

I am afraid of airplains...but this is nice...I love the sky and these clouds...Good job..