You have a cut vslley and not a woven valley.

Cuts are more vulnerable to leaks.

In the woven the shingles continue all the way across the valley.

The cut could be a little narrower, but without a scale i the pictures it is hard to tell.

You might want to get some tar and stick down the edges a little better.

Thanks. I found a staple under a shingle that looked a little loose, so I tarred it and nailed it back down, and tarred some of the other shingles, too. Hopefully this will help.

You might try backing up a bit when you take a photo.

In your "shinglecutwrong1" photo, we'll cut that little triangle off. Removing those triangles is called "dubbing". Those pointy ends can help channel water further away from the open valley.

Not sure if this link I'm adding will lead to just the pdf, or if it will lead to the specific page. Regardless, check out page 64 of this.