saving images for prints

terri

I'm having a problem when it comes to saving my images for printing. Most come out fine, but some I just don't know. I had one picture that the machine cropped on me. The feet, bottom, tail, and side of the photo were cropped off. I tried making the image smaller, but still the same results.
What I'm selecting is image size, then I enter width 6" height 4".

Could someone just tell me step by step on how to save an image for printing? I am so confused. I don't understand how I can plug my memory card right into the picture machine and have no problems, but when I try to put an edited image in the machine I'm having problems. The edited image is way smaller than the one straight off the memory card. I am using photoshop. Any help would be greatly appreciated!