When young common snappers often have the more rigid shell, it will fade as it grows. I had the same thoughts with one of mine and he turned out to be a chelydra serpentina osceola. He's still about the size of a softball and has the ridges, I'll see if I can post pics sometime this weekend. Here's a young common snapper showing the ridgid shell
Also, look at the color, pattern on the face of yours, nothing like the face of an ally.
Look at the beak and how large the ridges are on this ally.

Also, look at the color, pattern on the face of yours, nothing like the face of an ally.
Look at the beak and how large the ridges are on this ally.