Help with bo in middle of row

I am making the booties found here:

I am stuck on the last “Shape top” row where it says to "bind off 7 sts, K3 and slip to holder, bind off 3 sts, k7.
When I bo, I end up with a stitch left on the right needle and I don’t know what to do with it. Am I binding off wrong?

Depending on how many stitches there are, you knit the next stitch, the pass the bind-off stitch over the knit stitch. You count that as the first knit stitch.
In some patterns, the last stitch on the needle after binding off is counted as the first knit stitch.

That makes total sense! You are a lifesaver.

Making these booties:

In the section called Strap, after Row 3, it says “Bind off”. Am I to assume I should bind off everything on my needle? Then it says to move sts fom stitch holder back onto the needle and “join yarn”. How do I do that?

I assume you have stitches on the stitch holder by then. So when it says to bind off, you bind off all the stitches on the needle. You cut the yarn.

Then you move the stitches from stitchholder onto the needle and “join” the yarn, which you can do by just holding the yarn like you normally would, with the loose end close to the needle, then you knit normally. (Can be a little bit tricky to pick up the loose yarn, but should work)

Without the pattern of course, it’s hard to tell what exactly you have to do.