Knitting a seam

I am knitting my first project (some booties) and the pattern I have Debbie Bliss baby cashmerino doesn’t really explain everything so well. The bottom line is I’m stuck. I’ve knit the top of the bootie, the heel and the sole but the pattern would seem to have me run a seam along the middle bottom of the sole. This seems like it will be awkward to wear later and I’m wondering if I have followed the pattern correctly.
The pattern states to "Join sole and back heel seam. With right side facing, beg and end within 9 sts of back seam. K up 18 sts along heel for ankle strap.
When it says join sole and back heel seam would you take that to mean the bootie’s sole and heel should already be knit together?
I’m so lost.
Thanks for any replies.

I have not used the pattern you mentioned, but I did make some booties that sound similar. Mine worked out that you did indeed have a seam up the center of the sole of the bootie and then up the back of the heel (much like a shoe.)

Post a photo - maybe if someone sees the piece they can give you a more accurate diagnosis!