Dividing for heel

I have a strange problem and I can’t figure out what I’ve done.
My pattern says to: P across the back of the heel flap, slipping the first stitch.
Sl1 K1 across.
Repeat these 2 rows till you have worked 28 rows (count the sliped stitches which should be 14.

For some reason I ended up with 14 slipped stitches on one side and 12 on the other. I couldn’t find any place where I had failed to Sl1.
What have I done?:frog:

If I understand you correctly it appears that you are slipping stitches on both sides. What you do is alternate rows. One Purl row where you slip the first stitch only then purl across the remaining stitches. The second row is K1, S1 all the way across ending with a K1.