Don't worry that file size is larger than specified that it should be. Save the image as jpeg, and then have a look at it in its folder and you will see that it is, in fact the file size you wanted. Use lower resolution than 300, usually 75, but keep the 1000px shortest side. I assume that this is a spec for entering image for exhibition, and they usually want 75dpi, unless otherwise specified. They usually give very poor directions for accomplishing what they are asking for!
