It's a 4 stitch repeat as you've written it out, repeated about 60 times across the row. I don't think you're doing anything consisently wrong, maybe just forgetting to pass the slipped stitch over on some of the repeats. Take a look at the last row of the repeat and see if you can name the stitches across the row. There should be the increase in the single stitch and then the double decrease. You may need to rip back to the best row that you have and start the pattern area again. Adding in a lifeline
will help in case this happens again and maybe stitch markers every 40sts just to make counting easier.