Hello Mat and welcome!
Stitching images is a tricky procedure. stitching softwares are all different, but generally they rely on the same image characteristics to create a good panorama:
-good image overlay
-visible features easily recognized
-bright, contrasty scenes
That means, for instance, that pictures of the sea taken at dusk will not stitch easily. Generally, stitching programs need at least three points to make a good stitch, and ideally these points should be disposed in a triangle, not a line.
Regarding your images, since you say you took them into your backyard, I'm guessing the images have both near and far elements (nearby trees, the sun far away, for instance). That's one of the hardest things to stitch, because the perspective becomes wrong. I don't know of any foolproof software that takes care of these situations.
You could try stitching the images manually, if you have a program that supports layers (such as Photoshop). You could also try other free programs, such as Hugin. Autostitch is generally seen as a good program, but another program could perform better in your specific situation. Cameras generally come with software for stitching, that might be worth a try.
I had not enough time to work at my panorama, but I have a small question: how to raise the contrast of the photos without using Photoshop, because I don't have it?
